[boppo1]

What is a 'book' in the context of trading?

[jll29]

short for "orderbook" - the set of pending trades pertaining to a client account

[bitcharmer]

No, it's most often not related to any particular client. Rather the book is a list of all buy and sell orders that didn't match sitting there and waiting for someone to take the other side of the trade

[grumpyprole]

Just an old name for a portfolio of transactions

[0x264]

Set of related trades.