Black plastic cap under car

[spookybathtub]

While changing my transmission fluid, I noticed this under the car. It's a black plastic rectangular cover, and it's easily removed with a fingernail. Looks like it's on the far right side of the transmission. This photo was taken from underneath the passenger wheel. Can anybody tell me what it's for? Since it comes off so easily, I figure maybe it's intended for regular maintenance, but I can't figure out what I'm looking at inside —*it's pretty grimy though.

[CTScott]

It is an inspection port for looking into the clutch or torque converter housing.

[spookybathtub]

Alright then I'll just forget about it. I think that's over my head.