Random tidbit of information, as I see people using this term rather loosely everywhere:
A TFSA is an registered investment account, and doesn't necessarily mean a guaranteed principle or interest rate. Much like an RRSP, money that you have in a TFSA can actually be invested in stocks, bonds, mutual funds, GICs etc.
It just so happens that the majority of people, especially students, that have a TFSA only choose to place it in a savings account in a consumer bank that offers a guaranteed (but low) interest rate. The guaranteed principle / interest comes from the bank's savings account that they default people's money into when they open a TFSA, not the TFSA itself.
An interesting read:
http://business.financialpos t.com/2013/06/11/you-want-to-talk-value-investing-try-to-top-this-guys-tfsa/?__lsa=4c8a-bfe9
This guy made a ton of money in his TFSA by investing in penny stocks. No way you can get those kind of gains in a guaranteed interest savings account