Blueprints are plans to create an items in the Eve universe. An industrialist can use a blueprint and raw materials to run a manufacturing job at a station's factory to create finished goods.
You can calculate manufaturing time and required materials for a blueprint using the EvE BPO Calc Tool.
BPOs can be used an infinite number of times. Almost all BPOs are for Tech 1 items. BPOs are originally sourced from NPCs although they can be sold by players on the market as well as through contracts.
BPCs can only be used a certain number of times. After the maximum number of runs has been completed, the BPC disappears. BPCs can be created by copying a BPO.