These concepts tend to apply more to the NetQ CLI than the UI, but the terms are used throughout the documentation and product.
A check is an on-demand validation of various elements in your network fabric at the current time or a time in the past. Such elements include the NetQ Agent, various protocols such as BGP or OSPF, and configurations like interfaces or EVPN.
A trace verifies network connectivity on-demand between two devices at either layer 2 or layer 3.
A show command is used for monitoring both hardware and software.