Jellyfish are plankton (from the Greek word planktos, meaning to wander or drift) and are not strong swimmers, so they are at the mercy of the ocean currents. Blooms often form where two currents meet and if there is an onshore breeze thousands of jellyfish can be beached.
When huge numbers of plants or animals appear suddenly, scientists call it a 'bloom'. In some areas of the world, millions of jellyfish can swarm together, and these blooms cause problems for fisheries and tourism. If you've been at the beach or on a boat at some point when it seemed like jellyfish were everywhere – then maybe you have even seen a jellyfish bloom.
The word jellyfish is a common term used to describe animals that are gelatinous or made up of ‘jelly-like’ material. There are many different types of jellyfish, including stinging kinds called medusae and non-stinging kinds called comb jellies or ctenophores. Another type of jelly animal called a salp is even in the same group as humans!