I've never seen butter in a tub before. We get weird "spreadable" vegetable-based butter substitutes in tubs. Some British people call it margarine but that's incorrect as margarine comes in solid blocks like butter (it's uncommon these days as it's no longer really needed).
In the US we have "whipped butter" which (according to Wikipedia) is made spreadable by aerating it with nitrogen. I recall hearing that it isn't suitable for situations that require measuring because the volume is not the same. (But it does works well on bread or for greasing a pan.)
