Approximate, Outline, Gist
Noun
だいたい
大体あっています。
That’s about right.
大体同じぐらいのせです。
We are about the same height.
私は大体6時に起きます。
I generally get up at 6 o’clock.
If all you can see is a big body of a person, then you'll only have a general idea of what they look like. You know their outline is quite big, but you don't know anything else.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.