The phrase "flexibility is relative" means that the concept of flexibility is not an absolute, fixed characteristic, but rather it is dependent on or compared to certain factors or contexts. In other words, how flexible something or someone is can vary depending on the situation, the criteria being considered, or the standards being applied.
For instance, if you're talking about a material's flexibility, it might be flexible compared to one material but not as flexible when compared to another material. Similarly, when discussing a person's flexibility, it could refer to their adaptability in different circumstances or their ability to change their opinions or behaviors based on the situation.
The idea of relativity in flexibility emphasizes that flexibility is not a one-size-fits-all concept but should be understood within a specific context or in comparison to a particular reference point.