What is "gave a nervous wave,"?
He saw you, "gave a nervous wave,"

If you are nervous, you are frightened or worried.

give a wave is the same as greeting with hands.

So what nervous wave says is to wave him with nervousness?

Question

What is "gave a nervous wave,"?
He saw you, "gave a nervous wave,"

If you are nervous, you are frightened or worried.

give a wave is the same as greeting with hands.

So what nervous wave says is to wave him with nervousness?

Answer

Yes, if you 'give a nervous wave' you wave your hand (to say 'hello' or 'goodbye') in a nervous way. An onlooker could tell that the person was nervous by the way that they waved.