TCP/IP and TCP and IP difference?

When TCP and IP are mentioned separately then they mean a transport layer (RFC 793) and a network layer protocol (RFC 791) respectively. But when mentioned in TCP/IP format they mean a stack which TCP/IP suite.

In the following link you may distinguish the two models OSI and TCP/IP: http://electronicdesign.com/what-s-difference-between/what-s-difference-between-osi-seven-layer-network-model-and-tcpip

In case of TCP/IP model, it supports other protocols in different layers than 4 and 3, but also TCP protocol could be replaced by UDP or STCP and it will still remain as TCP/IP model.

TCP/IP is a protocol stack which contains different protocols required for the data transfer from sender to receiver. In this the IP denotes the Layer 3 protocol which is connectionless and does not have error recovery procedure. So Layer 4 protocol comes into role to give reliability and help to recover the lost packet. UDP is also a protocol in this stack.

IP - Network Layer protocol for logical addressing.

TCP - Layer 4 protocol which ensures reliability and is connection oriented.