(noun)
in informal American usage, a person who is unreliable or eccentric;
e.g. He is a flake who tends to abandon plans at the last minute.
(noun)
in archaeology, a type of tool used by prehistoric humans, made by chipping off a piece of hard stone (usually called "flake tool");
e.g. He discovered a type of flake tool that he had never seen before.
(verb)
to break off from a surface in small, thin pieces, or to cause something to break off or separate in this manner;
e.g. Dirt began to flake off the gate as I scrubbed it. Use a fork to flake the fish to see if it is cooked.
(verb)
in informal American usage, to be unreliable and fail to fulfill a commitment or keep an appointment, especially with little to no prior notice;
e.g. They always flake on our plans and fail to attend at the last minute.