For feeding syrup to bees
Many types of feeder exist, but in the main they follow similar principles of providing a liquid feed in a protected enclosure so that bees or wasps are not able to access it.
As with many other items of beekeeping equipment the different types often bear their originator's or modifier's name.
Drowning of bees is a problem in some feeders and can give rise to rapid propagation of nosema. This is overcome by the use of some sort of cover to allow the syrup to flow through, but so the bees cannot penetrate. Feed should never be given to bees without the cover being put in place.
Frame feeders are the same size as a brood frame and can replace one in the brood box. There is usually a float inside to prevent the bees from drowning. Some beekeepers, especially those with out apiaries, have these permanently in the brood box in case a colony runs short of food. Some polystyrene nuc boxes have a feeder similar to a frame feeder moulded into the box.
I have not used frame feeders very much as I have not found them very successful. If they are left in the brood box I found the bees built comb in them and the queen laid in it. Wooden ones can leak, but they can be made in plastic now. To me they seem a good idea, but not very practical.
For those who are able to make their own equipment the "Bro. Adam" type feeder is probably the easiest to make, but it will need sealing to prevent leakage.
The plastic bucket type with wire gauze in the lid, the so called "contact" feeders are very commonly used, but being plastic can degenerate, become brittle and leak if left in the light. Covering up or putting inside a bin liner prevents that. One major problem I have had with plastic contact feeders is there are so many sizes that are all very similar, making it difficult to match the lids with the buckets.