Transfer
Transfer refers to the amount of data you can transfer to and from your server. In the web hosting industry, the word "bandwidth" is also used to describe transfer. "Transfer," short for "data transfer," is measured anytime a file is uploaded/downloaded to/from your account.
Every time that file is downloaded/uploaded, the equivalent of the space it takes is subtracted from your remaining transfer. If a file downloaded from your website is 100MB in size, then 100MB of transfer will be deducted from your monthly allowance.