A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch. Glass Petri dishes can be re-used by sterilization; plastic Petri dishes must be disposed of after one use.
For microbiology, agar plates are very frequently used. The dish is partially filled with warm liquid agar, a growth medium, along with a particular mix of nutrients, salts and amino acids and, optionally, antibiotics. After the agar solidifies, the dish is ready to receive a microbe-laden sample.
Definition from Wikipedia.