I was taught they were 4 in TCP/IP mapped as follows over "iso/osi" layers, example of protocols between square brackets:
ISO/OSI TCP/IP (extended) Data unit's name (ISO-OSI)
Application -> Application [telnet] => Packet (APDU)
presentation -> Application => Packet (PPDU)
Session -> Application (Security) [TLS]=> Packet (SPDU)
Transport -> Transport [TCP/UDP] => Segment (TPDU)
----------Above this line the communication is end to end-------------
Network -> Network [IP] => Datagram (Packet)
DataLink -> Host To Network => Frame (Frame)
Physical -> Host To Network (Bit)
Answering your question the TCP/IP model has 5 layers: Application, tansport, network and host-to-network. But I'd add the 6th layer as now more and more common TLS security because it has it's own identifiers and is a layer between TCP and application.
I can remember this by finding the "identifiers" for each data unit relatively to more used connections:
Application has application defined ID
(TLS has [implicit] message sequence number)
TCP has segment sequence number
Network has IP address
H2N has MAC address
This makes, in my opinion, HTTPS as an example of "session" level (I'd call it "security" level because there is where most security operations could be bundeled) because each TLS connection has its own identifiers and is incapsulated into TCP segments.