What is meant by terms like Sealing, InstantSeal, ManualSeal, etc. (please add them here if you know more kinds of seals).
Sealing a block means adding some final consensus-related information to a block to complete the block authoring process. Sealing happens on the client-side after all transactions have been executed and and other runtime logic has completed.
When other nodes in the network import your block, they will check the seal before checking other more computationally-expensive parts of the block such as executing transactions.
The exact information included in the seal depends on the consensus engine. In PoA and PoS consensus the seal is a signature. In PoW it is the mining output.
Because sealing a block usually the final step in authoring a block, people sometimes speak of "sealing" when they are really referring to the larger authoring process. This is the case for both manual seal and instant seal. The misnomer is particularly bad in this case because manual and instant seal don't actually use a cryptographic seal. A more accurate name would be "manual authoring" and "instant authoring". Learn more about what they are in What is the difference between Babe, Aura, and Grandpa?