The word of the day is ‘Empty sets’. They are called empty because outside of the quarterback, nobody is in the back field. They can be run out of shotgun or from under center. They are predominantly passing formations, although a few runs can be worked into the mix.
The first two sets in the graphic below are with the QB under center. The first example has a RB split out in a slot and two TEs on the field along with two WR (X & Z). The 2nd set is a slightly different look with two TE in wing positions off of the tackles, a Y receiver in the slot and X & Z out wide.
The bottom two examples are from the shotgun. The 3rd overall example has a pair of TEs on the field and one off to the left in a “Bunch” formation. it is called a Bunch formation because the trio of receivers are bunched together. The other TE is in a normal position and the Z receiver is off the LOS to the right. The 4th and final example is a pure 5-wide receiver set with 5 wide receivers on the field.