What is the differece between snmp, snmpd and snmptrapd?

I am new to the SNMP protocol.
I try to configure SNMP-traps for Zabbix but I am confused what daemons I have to use. I need to install snmptrapd, but somehow snmpd is required for that:

sudo apt install snmptrapd
Reading package lists... Done
Building dependency tree       
Reading state information... Done

The following additional packages will be installed:
  snmpd
The following NEW packages will be installed:
  snmpd snmptrapd
0 upgraded, 2 newly installed, 0 to remove and 75 not upgraded.

What is the relationship between these 2 packages? Am I right that these 2 are daemons?

And what is inside the Ubuntu SNMP-package? What's the relationship between the snmp and snmpd packages?