Ranchero is a Mexican culinary term that means "country style" or "of the ranch". A popular sauce named "ranchera sauce" or "salsa ranchera" is made from onions, chiles and fresh tomatoes. The sauce is traditionally used over huevos rancheros. Here is recipe for a simpler ecipe for salsa ranchera.
The chiles used vary per recipe but jalapeno, serrano, ancho and even fresh poblano chiles may be used.
You can use the sauce for making enchiladas or use it to top chiles rellenos. Use it to top taquitos or even a simple quesadilla.