There are 4 types of graphs:
Active - useable graph
Archived - kept and can be retrieved at a later date
Delete - gone forever
Hidden - doesn't show up in Search or Data Entry but can be used as part of the formula in a calculation graph or as the Key Result of an Objective.
Active, Archived and Hidden graphs are used to calculate your monthly subscription value.
How to Hide a Graph
See step 14 in Edit a Graph.
When you want to find Hidden graphs see How to Find all Graphs Types.