Shopper
A consumer sometimes is a kind of participant or function in a distributed software construction known as client-server. Shoppers talk with servers and never with different shoppers.
Server
Servers primarily talk with shoppers and never with different servers. When servers talk with different servers they could use a special protocol (e.g. SMTP as an alternative of IMAP/POP) or in any other case act as a consumer as an alternative of as a server in that relationship.
Node or Peer
A node is a peer in a peer-to-peer community. The concept right here is that every one friends have the identical function and tasks. Their roles will not be differentiated.
Bitcoin
The Bitcoin community was designed as a peer-to-peer community. Not as a client-server community.
Bitcoin core
Strictly talking, calling a program similar to bitcoin-qt a consumer is misusing client-server terminology for peer-to-peer distributed-application construction.
bitcoind is a server (for the RPC API) however notice that bitcoin-qt is not a consumer for bitcoind at current.
bitcoind and bitcoin-qt are each nodes or friends with respect to the peer-to-peer Bitcoin community protocol. Each are servers (not shoppers) with respect to the network-accessible client-server RPC API. bitcoin-cli is a consumer for that.
See associated query about constituent packages of Bitcoin Core