In the Wikipedia article, TCP communication is explained using the terms ‘client’ and ‘server’. It also uses the word ‘peers’.
But to my knowledge, the TCP standard does not define "TCP clients" and "TCP servers".
In the RFC 675 document (the "Specification of Internet Transmission Protocol Program"), the word "client" never appears. The RFC explains that TCP is used to connect processes over ports (sockets), and that ‘A pair of sockets form a CONNECTION which can be used to carry data in either direction [i.e. full duplex].
However, calling the originating party the "client" seems to be common practice. But IMHO this client/server communication model is not always applicable to TCP communication. For example take peer-to-peer networks. Calling all processes which open a socket and wait for incoming connections from peers "TCP servers", sounds wrong to me. (And I would not call my uncle’s telephone device a "Telephony server" if I dial his phone number and he picks up.)
TCP is only about connecting one process to another via a bi-directional, ordered byte stream. Talk of ‘clients’ and ‘servers’ describes a common usage pattern, but is external to the definition of TCP itself.