FYI OP, most bassist say tension when they mean stiffness. They also say tension when they mean tension. Basically because there needs to be an easy word to explain the way the strings flex when playing, and tension is at least a small part of it.
"Flexibility when playing" is really what we should be saying though, since that is the end result of a combination of tension of strings at pitch and stiffness of string design.
Basically if it's hard to move the string when playing, that is pretty commonly due to the stiffness of the string due to construction and design, although tension differences also affect that if they are great enough.
Now that I've muddied things up - have fun!
"Flexibility when playing" is really what we should be saying though, since that is the end result of a combination of tension of strings at pitch and stiffness of string design.
Basically if it's hard to move the string when playing, that is pretty commonly due to the stiffness of the string due to construction and design, although tension differences also affect that if they are great enough.
Now that I've muddied things up - have fun!