A database, in the most general sense, is an organized collection of data. More specifically, a database is an electronic system that allows data to be stored, accessed, manipulated and updated.
A ledger is a set of physical records, or electronic records, for example, a database, in which a company's accounts are recorded, especially the money it has spent and received.
As we’ve already learned, in computing, a network is a group of two or more devices that can communicate via physical and/or wireless connections. The two most common types of network architecture include peer-to-peer networks, also referred to as P2P networks, and client-server networks.
Decentralised networks or systems are those without a single-point-of-control and therefore failure e.g. a decentralized network does not a have a central server that could be maliciously tampered with to gain access to the entire network.
And finally, we have the term...
Not to be confused with decentralised. In Blockchain terms, this refers to the process by which ledgers are distributed amongst all members of the Blockchain network. To elaborate ledgers are not managed by one particular body; instead, everyone in the network gets a copy of the entire ledger, in the form of an electronic database.