Compost tea is a solution that improves the health of soil, which in turn improves the health of the plants that grow in that soil.
It is a liquid version of your compost. Howard Garrett the Dirt Doctor explains the basics here. He uses finished compost, and gives us pointers on what you can add for even more benefit. Adding fish emulsion/ fish oil or liquid seaweed will amplify the fungal activity. Adding molasses will kick up the bacterial action.
This form of liquid fertilizer gives you faster results, as the solution goes right into the foliage.