For the uninitiated, this is the Indian numbering system. To summarize, the system uses numbers in groups of 2 after the 1,000 instead of 3 digits like rest of the world.
This is curious to me considering the Arabic Numerals originated from India.
The wikipedia articles on this are pretty good: http://en.wikipedia.org/wiki/Crore
http://en.wikipedia.org/wiki/Lakh
http://en.wikipedia.org/wiki/South_Asian_numbering_system
To summarize briefly, Sanskrit (the ancient religious language of India) and Prakrit (collective term for vernacular languages from which the languages of northern India today descend) had specific terms for powers of ten. English has specific words for ten, hundred, thousand, and million; Sanskrit / Prakrit, in effect, add in specific words for ten thousand, hundred thousand, etc.
So lakh and crore survived from those languages, are now used in modern Indian English, and effect how numbers are grouped when they're written.