Here is the technical term for Tax Deduction:
To make this easy think of it this way:
Let's say you can be taxed at 10% a year.
You made $1000 in a year. All of that will be taxed at your 10%
Wait, you have $300 Deduction.
This means you will only be taxed on $700 of what you made.
Isn't as great as a Tax Credit but, it is good know and take advantage of.