In short, Lisk Core is the codebase of the rules established by the Lisk Protocol. It is a mandatory program to be executed on every node in the Lisk network, and guarantees the validity of the data contained within the Lisk blockchain and the new data being written on it.
Timestamps:
0:10 - 1:58 What is the client-server relationship?
1:59 - 2:52 How does a server become a Lisk node?
2:53 - 3:42 Who can run a node?
3:43 - 4:01 Why would someone set up their own node?
4:02 - 4:20 What is Lisk Core?