TA

• temperature (PIREP only)

  ATC

• total aboard

  General

• transition altitude

  ICAO

TA has 3 meanings; the right one depends on context. A weather report, a NOTAM or an ATC clearance. Got a NOTAM full of contractions? Paste it into the decoder.

Source: FAA Order JO 7340.2 Contractions. Not for operational use.