There are two elements that go into determining Paper Weight:
1) The TYPE of paper stock (ex. BOND, TEXT or COVER)
2) The WEIGHT of paper stock (ex. 60 lb, 130 lb, etc.)
Note, just because an item has a higher weight doesn't mean it's thicker.
Examples of use:
Bond stocks are often used for note pads.
Text stocks are often used for note pads, Post-It® notes, light-weight note cards, and medium-weight note cards.
Cover stocks are often used for medium-weight note cards, heavy-weight note cards, holiday cards, business cards and invitations.
Board stocks are similar to cover stocks except they are available in much heavier weights. At 60 pt., board stock is extremely rigid and thick, similar to the cover of a harcover book.
Further information for paper enthusiasts
So, why isn't 80 lb. Text the same weight as 80 lb. Cover?
While the weight in pounds for most paper types is based on the total weight of 500 sheets, the dimensions of each individual sheet may vary for different TYPES of paper stock.
For example, Text stock is weighed based upon 25" x 38" sheets, while Cover stock is weighed based upon 20" x 26" sheets.
Due to manufacturing differences in paper, not all papers of the same type and weight will feel the same.