The Dictionary Definition of Transient is
"passing especially quickly into and out of existence"
Transient currents are very brief events where channels gate a brief current.
How to interpret them? It depends on the channel type you are studying.
Normal parameters to analyze would include
Peak amplitude
Time to peak
Time constant of activation
Time constant of deactivation
Time constant of inactivation/desensitization
Voltage dependence
EC50 for agonist/cognate ligand