Compost tea is a liquid extract or dissolved solution made from compost. It is not a suspension of compost - instead, it is made by steeping (suspending a bad of compost in water - rather like making tea from a tea bag).
The process and treatment was discovered in Germany and found application in disease control - especially fungi, by encouraging bacterial competition. It can also be used as a fertilizer but tests have shown it to be a very weak fertilizer.
Application is typically by spraying on to non-edible plant parts or by drenching the soil (e.g. as a "root dip" or surface spray).
Use this tag for all questions about making, using, and effectiveness of compost tea.