If you want the dictionary definition, just double click on any word.
a lot or allot

A lot, meaning a large amount or number of people or things, can be used to modify a noun.

For example:-

"I need a lot of time to develop this web site."

It can also be used as an adverb, meaning very much or very often.

For example:-

"I look a lot like my sister."

It has become a common term in speech; and is increasingly used in writing.

Allot is a verb, which means to give (especially a share of something) for a particular purpose:-

For example: "We were allotted a desk each."

!Note - Many people write a lot as one word "alot", probably because it is pronounced like one word. However it does not exist! There is no such word in the English language. If you write it this way - imagine me shouting at you - "No Such Word!"