What is a teaser exactly?
A teaser is a combination of two or more football/basketball spreads/totals where you get a better line on each pick in exchange for a lower payout. There is an incredible number of variations in how teasers are offered (we'll discuss why later) but generally you can tease your football lines 6, 6.5, or 7-points and your basketball lines 4, 4.5, or 5-points.
For example if you like the Eagles -8 and the Chargers +2 but aren't sure the Eagles will win by a touchdown or the Chargers will keep it close you could tease both these picks. If you teased 7-points you would have a 2-team teaser with Eagles -1 and the Chargers +9. I think you can clearly see that making Philadelphia only have to win by 2 to cover (instead of 9) makes this bet easier to win. Also, the Chargers can now lose by 7 and still cover. The tradeoff is the payout is only 10/13 (this varies from book-to-book but will serve for our examples today) instead of 13/5 as a parlay would be. If you risked $65, the teaser pays $50 but the same two picks in a parlay would pay $169. You must decide if the greatly improved chance of winning is worth a 2/3 reduction in payout.
With teasers involving three or more picks, a push on any leg reduces the teaser to the next lowest level. A 4-teamer where one leg is a push would payout at 3-team levels, etc. Note that a 2-team teaser with a push is not reduced to a 1-team teaser as there is no such bet. Be sure to check with your book to see how 2-team teasers with a push are handled (some settle push/loss as a loss, others make it a push) so you are not surprised.