Serrano chillies
From Cookipedia
The serrano pepper (Capsicum annuum) is a type of chili pepper that originated in the mountainous regions of the Mexican states of Puebla and Hidalgo. Unripe serranos are green, but the colour at maturity varies. Common colours are red, brown, orange, or yellow. Serranos are very meaty and thus they do not dry very well. They are generally between 1 and 4 inches long (2.5 to 10 cm) and around ½ inch (1 cm) wide.
Most serranos rate between 10,000 and 20,000 Scoville units.
Nando's Hot Extra Hot Peri-Peri Sauce is once of many commercial products made with serrano chilies.