what is "bid size" on Time and Sales

I'm watching it after hours on the ES and I see one row that says:

Volume: 1 BidSize: 7

And another row where the volume is higher:

Volume: 15 BidSize: 2


I assume volume is how many were sold at that price.

What is bidsize? How many they were trying to sell? How could that be less than the volume then?

 

The bid-size you see is often not the acutal bid-size - there are hidden orders.

Do some research on the variety of order types

 

Ok but what is bidsize? Was my original guess correct?