What is the meaning of Cracker?

A noisy boaster; a swaggering fellow.

A dry, thin, crispy baked bread (usually salty or savoury, but sometimes sweet, as in the case of graham crackers and animal crackers).

A prawn cracker.

The final section of certain whips, which is made of a short, thin piece of unravelled rope, or which is a short piece of twisted string tied to the end of the whip, which produces a distinctive cracking sound when the whip is cracked.

A firecracker.

A Christmas cracker.

A northern pintail, a dabbling duck of species Anas acuta.

A person or thing that breaks a thing (e.g., nutcracker).

Refinery equipment used to pyrolyse organic feedstocks. If catalyst is used to aid pyrolysis it is informally called a cat-cracker

A pair of fluted rolls for grinding caoutchouc.

One who cracks (i.e. overcomes) computer software or security restrictions.

A fine, great thing or person (crackerjack).

(Discuss this sense) An ambitious or hard-working person (i.e. someone who arises at the 'crack' of dawn).

An impoverished white person from the southeastern United States, originally associated with Georgia and parts of Florida; any white person (slang).

(Can we verify this sense?) A police officer.

alternative form of krekr

drug user

Source: wiktionary.org