wall-to-wall carpet (=cut to fit a room): There was a green wall-to-wall carpet in the hall.
2.rug: a small carpet that covers part of a floor
ex.a rug in front of the fireplace
3.blanket: a thick cover made of wool or another material that you use to keep warm in bed
4.mat: a small piece of thick rough cloth that is put on a floor to protect it or for decoration；或者 A flat piece of coarse fabric or other material used for wiping one"s shoes or feet, or in various other forms as a floor covering.
如果從美式英語的角度上面來講，
1.carpet: a thick soft cover for a floor
wall-to-wall carpet (=cut to fit a room): There was a green wall-to-wall carpet in the hall.
2.rug: a small carpet that covers part of a floor
ex.a rug in front of the fireplace
3.blanket: a thick cover made of wool or another material that you use to keep warm in bed
4.mat: a small piece of thick rough cloth that is put on a floor to protect it or for decoration；或者 A flat piece of coarse fabric or other material used for wiping one"s shoes or feet, or in various other forms as a floor covering.
從上面可以看出來，第一個carpet是指那種覆蓋了整個房間的地毯。
而第二個是這小的地毯，比如我們中國放在每個房間門口的那種小塊地毯，或者美華人壁爐前的小塊地毯。
第三個一般是指你用來蓋在身上的被子。
而第四個是指比較粗糙的材料做成的地毯，鋪蓋地面或者擦鞋用。個人理解這種毯子主要強調其用途是防地板腐蝕或鞋子變髒，而並非裝飾類用途吧。
當然，每個毯子都還有其它含義，但是主要的意思就是這個了，如果你到美國，沒有上下文說出這些單詞，他們肯定都認為是這種意思了。
另外我建議你以後遇到這種不能去分的情況，就去檢視英英解釋吧，那樣你自然就知道了他們的區別。祝進步~