Is there a standardised way to refer to a specific terminal within an airport?

There is no unique identifier code for airport terminals. Each airport has its own system for designating facilities as terminals or for their naming. Most commonly, separate terminal facilities are numbered and letters are assigned to airside concourses (which may be called as piers, airsides, or modules among other terms); however, there is significant variation due to differences of layout and services.

Some examples are provided below; major airports with only one terminal, such as London Stansted or Bangkok Suvarnabhumi, are omitted.

Major Connecting Hubs

AMS  Amsterdam Schiphol             1 (B,C), 2 (D,E), 3 (F,G,H,M)
ATL  Atlanta Hartsfield-Jackson     T,A,B,C,D,E,F
AUH  Abu Dhabi                      1,2,3
BCN  Barcelona EL Prat              1, 2 (B,C)
BOG  Bogotá El Dorado               1, 2, 3
BOM  Mumbai Chhatrapati Shivaji     1A, 1B, 1C, 2
CAN  Guangzhou Baiyun               A,B
CDG  Paris-Charles De Gaulle        T1, T2 (ABCDEFG), T3
CGK  Jakarta Soekarno–Hatta         1 (A,B,C), 2 (D,E,F), 3
CLT  Charlotte Douglas              A,B,C,D,E
DEL  New Delhi-Indira Gandhi        1 (A, C, D), 3
DEN  Denver                         A,B,C
DFW  Dallas-Fort Worth              A,B,C,D,E
DME  Moscow Domodedovo              A,B
DTW  Detroit Metro Wayne County     McNamara (A,B,C), North (D)
DUB  Dublin                         1,2
DXB  Dubai                          1,2,3,4
EWR  Newark Liberty                 A,B,C
FRA  Frankfurt                      1 (A,B,C,Z), 2 (D,E)
GRU  São Paulo Guarulhos            1,2,3,4
HND  Tokyo Haneda                   1,2,International
HKG  Hong Kong Chek Lap Kok         1,2,NSC
IAD  Washington Dulles              Main (Z), A, B, C, D
IAH  Houston Bush Intercontinental  A,B,C,D,E
ICN  Seoul Incheon                  Main,A
IST  Istanbul Ataturk               1,2,3
JFK  New York John F Kennedy        1,2,4,5,7,8
JNB  Johannesburg OR Tambo          A,B
KIX  Osaka Kansai                   1,2
KUL  Kuala Lumpur                   Main (MTB), Satellite A, klia2
LAX  Los Angeles                    1,2,3,4,5,6,7,8,B ('B' aka TBIT or Tom Bradley International Terminal)
LGW  London Gatwick                 N, S
LHR  London Heathrow                1,2,3,4,5
MAD  Madrid Barajas                 1,2,3,4
MEX  Mexico City Benito Juárez      1 (North, South),2
MIA  Miami                          North (D), Central (E,F,G), South (H,J)
MSP  Minneapolis-Saint Paul         Lindbergh (A,B,C,D,E,F,G), Humphrey (H)
MUC  Munich                         1 (ABCDE, F), 2 (G,H)
MXP  Milan Malpensa                 1 (A,B,C), 2
NBO  Nairobi Jomo Kenyatta          1A, 1B, 1C, 1D, 1E
NRT  Tokyo Narita                   1 (North, South), 2, 3
ORD  Chicago O'Hare                 1 (B,C), 2 (E,F), 3 (G,H,K,L), 5 (M)
PEK  Beijing Capital                1,2,3 (C,D,E)
PHL  Philadelphia                   A (E,W), B, C, D, E, F (1,2,3)
PHX  Phoenix Sky Harbor             2, 3 (North, South), 4/Goldwater (A,B,C,D)
PVG  Shanghai Pudong                1,2
SEA  Seattle-Tacoma                 Central (A,B,C,D), N, S
SFO  San Francisco                  1,2,3,International
SHA  Shanghai Hongqiao              1,2
SIN  Singapore Changi               1,2,3
SVO  Moscow Sheremetyevo            NORTH: A [Business and private] B [previously Sheremetyevo-1, Domestic low-cost/cargo] C  
                                    SOUTH: D [at one time Sheremetyevo-3] E [with D used by Aeroflot and SkyTeam partners] F [previously Sheremetyevo-2]
SYD  Sydney Kingsford Smith         1 (International),2,3
TPE  Taipei Taoyuan                 1,2
TXL  Berlin Tegel                   A,B,C,D
YVR  Vancouver                      Main-Domestic (A,B,C), 
                                    Main-International (D,E), South
YYZ  Toronto Pearson                1,3
ZRH  Zürich                         A,B,E

Other Major Tourist Airports

AKL   Auckland                      Domestic, International
ARN   Stockholm Arlanda             2,3,4,5
ATH   Athens Eleftherios Venizelos  Main (A,B), Satellite
AYT   Antalya                       1,2,3
BOD   Bordeaux                      A,B,Billi
BOS   Boston Logan                  A,B,C,E
BRU   Brussels                      A,B
BWI   Baltimore Washington Marshall A-B, C, D, E
CAI   Cairo                         1,3
CPH   Copenhagen                    2,3
CUN   Cancún                        1,2 (Main, Satellite)
DAR   Dar es Salaam Julius Nyerere  1,2
DCA   Washington Reagan National    A, B-C
DMK   Bangkok Don Mueang            Domestic, International
DPS   Denpasar Ngurah Rai           Domestic, International
DUS   Düsseldorf                    A,B,C
EZE   Buenos Aires  Pistarini       A,B,C
FCO   Rome Fiumicino (da Vinci)     T1,T2,T3,T5
FLL   Fort Lauderdale-Hollywood     1 (B,C), 2 (D), 3 (E,F), 4 (H)
GIG   Rio de Janeiro-Galeão         1 (B,C), 2 (A,B,D) 
GVA   Geneva                        T1/M (A,B,C,D,F), T2
HAV   Havana José Martí             1,2,3,5
HKT   Phuket                        1,2
HNL   Honolulu                      Main (Diamond Head, Central, Ewa), 
                                    Interisland, Commuter
ITM   Osaka Itami                   North, South
JED   Jeddah King Abdulaziz         North, South, Hajj
LAS   Las Vegas McCarran            1,2,3
LGA   New York LaGuardia            A, B (A,B,C,D), C, D, Marine Air Terminal
MAN   Manchester                    1,2,3
MCO   Orlando                       A (1,2), B (3,4)
MDW   Chicago Midway                A,B,C
MEL   Melbourne Tullamarine         1,2,3,4
MNL   Manila Ninoy Aquino           1,2/Centennial,3,4/Domestic
MSY   New Orleans Louis Armstrong   B,C,D
ORY   Paris Orly                    South, West
PMI   Palma de Mallorca             A,B,C,D
PUJ   Punta Cana                    A,B
RAK   Marrakesh Menara              T1,T2
REP   Siem Reap                     Domestic, International
SAN   San Diego Lindbergh           1 (East, West), 2 (East, West), Commuter
SGN   Tan Son Nhat                  1,2
SJO   San Jose Juan Santamaría      Main, Domestic
SJU   San Juan Luis Muñoz Marín     A,B,D,E
SLC   Salt Lake City                1 (A,B), 2 (C), International (D,E)
SSH   Sharm el-Sheikh               1,2
SXF   Berlin Schönefeld             A,B,C,D
TLV   Tel Aviv Ben Gurion           1,3
TPA   Tampa                         A,C,E,F
VIE   Vienna                        1, 1A, 2, 3
WAW   Warsaw Chopin                 South (A,B), North (C,D,E)
YUL   Montréal Dorval               A,C
YYC   Calgary                       A,B,C

There are, unfortunately, no standards when it comes to naming the terminals. Numbers, letters, geographic direction, sub-letters/numbers, names are all in use somewhere.

Even single-terminal airports get an identifier if they have to be shoehorned into a reservation system. I often travel through "Vancouver Airport, Terminal 1/Main". CYVR has one building, the identifier implies otherwise. Given the distance between D50 and A22 it probably should be split.