I think that @GeorgeC
may be thinking something different. Here is what I think @regesullivan
Imagine that your board has two irregular sides that bend out slightly, like a somewhat oval shape. You want to turn your board into a regular board with two straight, parallel edges.
You can't press your board against a table saw fence and cut it, because both edges of the board are curved. That's dangerous, because the tiniest swing in either direction could cause a kickback. It's dangerous even if the edge is concave, because your board can move in the wrong direction when the end of your board passes the end of the fence and also cause a kickback. At best, the edge won't be straight.
The solution is to use another flat board with a known straight edge. It must be as long as your board. I will call it a "straightedge board." You could use a piece of hardboard, which is cheap and comes with a factory straight edge.
Clamp your board on top of the straightedge board so that one side of your board hangs beyond the straightedge board. There are different ways to clamp your board to the straightedge board. You could use double sided "carpet tape", for example. (The "usual places" didn't have it, including carpet stores. I found it at the local woodworking store.) Make sure that your board is tightly clamped to the straightedge board.
Place the straight part of the straightedge board against the table saw fence. Adjust the fence so that the blade will cut the side of your board farthest from the fence. Make sure your safeties are installed and ready, then rip cut your board by pushing the clamped boards across the table saw.
Remove your board from the straightedge board and put the straightedge board away. Flip your board over so that the new edge on your board is against the fence. Adjust the fence so that the blade will cut the other side of your board.
Now you have a board with two straight sides that are parallel to one another. They should also be square to the top/bottom surfaces.
Safeties: In addition to the blade guard, anti-kickback pawls, riving knife, splitter, push blocks, dust mask, hearing protection, eye protection, etc. etc. etc., think about featherboards. Also plan the safest way to stand and push the wood through the saw before
you make the cut.
I wonder whether my "straightedge board" is @regesullivan