a lot是一个短语,表示“程度”,有“很……,非常……”的意思。
a lot不等于many,当much修饰不可数名词时,a lot也不等于much. 
修饰比较级时,a lot等于much.
例句:
1、Thanks a lot.
 =Thank you very much.
2、Tom knows a lot about China
3、A plane is a lot faster than a bike.
=A plane is much faster than a bike.
a lot等于many还是much
一、many、much、a lot of的用法
many意思是“很多”,与可数名词复数连用
much意思是“很多”,与不可数名词连用。a lot of既可与可数名词连用,也可与不可数名词连用。它们在句中可作主语、宾语和定语等。
如:
I don’t have many friends here.在这里我没有很多的朋友
Many died in the bus accident.许多人在公交车祸中丧失
There was a lot of mud on the ground.地上有许多泥。
二、many、much、a lot of的区别
a lot of(=lots of)和many、much区别在于它们只能用在肯定句中,而many,much不受限制。
如果将一个含有a lot of(=lots of)的肯定句改为否定句或疑问句,要将它们改为many或much。
We can see a lot of birds in the tree.
We can’t see many birds in the tree.我们在树上看不到很多鸟儿。
He wants lots of soda.
Does he want much soda?他需要许多汽水吗