Thru or through
The word thru is an informal abbreviation for through, and hence not part of the standard English language. Therefore, it is not acceptable in formal writing. Interestingly though, thru has become so widely used that you can often see it used in internet communication and text messaging. And of course there is the drive thru, a crucial part of the American lifestyle (also referred to as a drive in). However, that term is not commonly used in Germany where, for example, McDonald’s calls its drive-in restaurant McDrive. (By the way, did you know that in some countries they have McWalks?)