If you are using a DSN-Less connection, then you must use a driver name that exists in your odbcinst.ini file. If you are using release independent odbc.ini and odbcinst.ini files then the default driver name to use is Teradata. Otherwise, for 16.20 and beyond, if you are using release dependent odbc.ini and odbcinst.ini files then the default driver name is Teradata Database ODBC Driver XX.YY where XX.YY is the version.
For example, ODBCINI=/opt/Teradata/client/17.20/odbc_32/odbc.ini then a successful connection would use a connection string like "DRIVER={Teradata Database ODBC Driver 17.20};DBCName=156.43.66.95;UID=username;PWD=password;".