What is the meaning of Sandbag?

A sturdy sack filled with sand, generally used in large numbers to make defensive walls against flooding, bullets, or shrapnel.

A small bag filled with sand and used as a cudgel.

An engraver's leather cushion, etc.

A deceptive play whereby a player with a strong hand bets weakly or passively.

To construct a barrier of sandbags (around).

To strike someone with a sandbag or other object to disable or render unconscious.

To conceal or misrepresent one's true position, potential, or intent in order to gain an advantage; to pretend to have a weak hand, as a strategy.

To blindside; to deceive; to undermine.

To pretend to drink early on so that, as the night draws on, one can drink everybody else "under the table".

Source: wiktionary.org