1 not confident and not knowing what to do in a particular situation: --
2 giving so much attention to what you are doing that you are not conscious of anything else that is happening around you: --
Ann was completely lost in her book.
3 (of a person) unable to find your way, or (of an item) not to be found: --
4 confused, or not able to understand or appreciate: --
Everyone else thought it was funny, but that joke was lost on me.
His explanation was so complicated, I got lost after the first example.
5 past simple and past participle of lose --
After three days lost in the mountains, all the climbers arrived home safe and sound.
He gazed pensively at the glass in front of him, lost in thought.
When you got lost in the forest you must have been very frightened.