BLS threshold key - split a key into a polynomial. Any shares more than the threshold are enough to reconstruct the signature.
key generation - algorithms that allow distributed key generation.
byzantine fault tolerance - system to decide what to sign.
SSV nodes - to put everything together + add a protocol for SSV nodes to speak to each other, validator clients, and beacon nodes.
SSV is a middle layer that comes between a beacon node and validator client. From the user’s perspective, it is just a component to plug in and take care of everything on their behalf. Essentially, a sophisticated multisignature wallet with a consensus layer.