The Oxford Dictionary of English records "piri-piri" as a foreign word meaning "a very hot sauce made with red chile peppers".
The African Birds Eye Chili is also called peri peri, pili pili, or piri piri.
It is a cultivar of Capsicum frutescens which is generally considered to have a smaller and hotter chili fruit than Capsicum Annuum, but truthfully there are precious little differences since there is a range of both sizes, colors, and hotness across both families. Again, more on *that* later. On to Piri Piri, or Peri Peri...
The spice blend Piri piri is Portuguese in origin and especially prevalent in Angola, Namibia, Mozambique and South Africa, used as a seasoning or marinade. It is made from crushed chili peppers, citrus zest, onion, garlic, pepper (piper nigrum), salt, bay leaves, paprika, pimento, basil, oregano, tarragon. If used as a sauce, it is usually mixed with lemon juice or another very acidic base to assist in the transfer of flavors.
In powder form Piri piri is excellent to add a big citrusy and earthy flavor to dishes as a finishing seasoning. It can be rendered into a sauce easily by adding lemon juice, lime juice, or tart wine to the powdered form. Diluting with water will reduce some of the tartness but make the seasoning go further in a marinade.
The African Birds Eye chile is considered to be Hot. It's rating is about 175,000 Scoville units, relatively akin to the more well-known Habanero.