There are 3 types of liquid we can encounter with compost or vermicompost. The word "tea" is sometimes used interchangeably when it probably should not.
Leachate has been discussed before here on The Blue Worm Bin, its the liquid that's created by a worm bin or compost pile that is too wet. This is the least reliable of the 3 liquids to use on plants. It may contain human or plant pathogen or compounds toxic to plants or it may be fine. If you opt to try leachate (at your own risk) it should always be deleted 10:1 or more with water
Extracts are really what previous generations called tea, To make an extract you place finished compost to vermicompost in a mesh bag, soak it in water and stir it vigorously every few hour. You remove the bag and use the leftover water on your plants.
My personal way to make an extract with vermicompost is a bit more involved but makes saving worm cocoons mucgh easier. I place vermicompost in a fine wire mesh basket and run the water over it into a bucket. The finest compost goes through the basket and the cocoons and larger pieces stay behind to be used to start a new worm bin.
The big advantage of extracts over leachate is; because its made with finished compost there is a far less chance of pathogens or toxins. The advantage over aerated teas is that the microbes remain in a similar ratio to the original compost.
Teas (aerated compost teas)
Aerated teas have become very popular over the last 30 years or so. Using an air pump with any of a number of brewer types and foods to increase the dissolved oxygen in the water and also increase the microbe levels to make a potent microbial additive. The advantages are that you can get a lot more "bang for your buck (compost)" with a much greater microbial biomass by volume. One of the advantages can also become a bit of a disadvantage in certain circumstances. Different foods added can drastically change microbe ratios and without some knowledge and a good microscope those changes in ratios may not be doing as much good as the could (they'll likely still be awesome so don't worry).
Hopefully this brief description helps clarify the differences between leachate, extracts or tea. I believe we should be more careful to discriminate which we are discussing in conversation.
Compost, Vermicompost and Compost Tea - $12.95
Part of the NOFA Guides Series. Information on composting techniques from the author of The Soul of Soil, Grace Gershuny.