The share of the property price you pay out of pocket at signing. Banks require a minimum of 10%, the sweet spot sits at 20-30%, and a larger enganche earns you a lower rate — paying 30% instead of 10% can shave half a point off your mortgage rate.
It's the part you put up yourself. On a car it starts at 10% to 20% of value; on a home, 10% to 20% for bank credit and sometimes less if Infonavit is involved. The more down payment you give, the less you finance and the less interest you pay — and you lower the risk of ending up «underwater», owing more than the asset is worth.
The quick math on a car: with 20% down instead of 10% on a 350,000-peso vehicle, you finance 35,000 less, which over 48 months at 16% CAT saves around 15,000 in interest. If you can stretch to the down payment, it almost always pays; the money «saved» by skipping it you end up paying back with interest.