What do ton ratings on pickups mean?

Way back when (1940s and 50s) the ratings meant what they sound like.

There were 1/4 ton 1/2 3/4 and 1 ton pickups

1/2 ton had 1000 pound carrying capacity and so on.

Somewhere in the 1950s this really lost its meaning. now it means a relative to the other trucks out there.