Last (I guess that's the word you are looking for) means load or burden, Gewicht rather weight such as the weight of a car or person. Translations without context are always difficult, but that should give you a rough idea.

Did you perhaps mean "die Last"?

Das Gewicht - is measurable (e. g. mg, g, kg, t). Die Last - is not measurable, it means something which is heavy or burdensome. It can be used both in literal and metaphorical meaning. Esel müssen oft schwere Lasten tragen. Wer schwere Lasten tragen muss, braucht die richtige Technik zum Anheben und Tragen, um keine gesundheitlichen Schäden zu nehmen. Diese Verantwortung zu tragen, ist für ihn eine schwere Last. Nachdem die Entscheidung getroffen war, fiel eine große Last von ihr ab.

Where have you heard or read "der Fast"? I've never seen it.

"fast" is a german word too, but it's an adverb and means "almost"