Abridged answer from stackexchange which explains the possible historical development of the name: I suspect the difference in usage is related to the difference in how usage of the various fruits developed in different parts of the world. Specifically, these plants are native to the Americas, where they were in cultivation long before Columbus arrived. They thus would have been first encountered by English-speakers in the Americas as a "going concern". The various fruits would likely have been a welcome and even necessary part of European Americans' (in the continental sense) culinary repertoire. Names for such common plants and foods would have been practical, and might have arisen from indigenous terminology (chili); analogy with known, old world ingredients (pepper); or descriptive terms (a "pepper" that is bell-shaped = bell-pepper). In other parts of the world, on the other hand, the plants would have first been known as exotic cultivars, and might have made their way into ordinary cultivation and kitchens by way of botanists, who would naturally be more concerned with precise terminology. Places introduced to the plants after this naming was established would be more likely to use it. The OED's evidence supports the hypothesis that pepper is the older English term for the fruits of genus Capsicum. The OED attests this usage to 1578: 1578 H. Lyte tr. R. Dodoens Niewe Herball v. lxix. 634 The Indian Pepper [Du. Peper van Indien, Fr. Poyure d'Inde] hath square stalkes. 1693 Philos. Trans. (Royal Soc.) 17 621 A long Pepper from Brazil. 1707 H. Sloane Voy. Islands I. 241 Bell Pepper. The fruit is large..somewhat shaped like a bell. . . . ("pepper, n." OED Online. Oxford University Press, June 2016. Web. 24 August 2016. Sense 3.) Capsicum, on the other hand, is first attested as a botanical term for the plant in 1664, and as a term for the plant's fruit in 1725. ("capsicum, n." OED Online. Oxford University Press, June 2016. Web. 24 August 2016.)

Extracted from Wikipedia: In Australia, New Zealand and India, heatless species are called "capsicums" while hot ones are called "chilli/chillies" (double L). In the United Kingdom, Ireland, and Canada, the heatless varieties are called "peppers", "sweet peppers" or "capsicums" (or "green peppers," "red peppers," etc.) while the hot ones are "chilli/chillies" (double L) or "chilli peppers". In the United States and Canada, the common heatless species is referred to as "bell peppers," "sweet peppers," "red/green/etc peppers," or simply "peppers", while the hot species are collectively called "chile/chiles," "chili/chilies," or "chili/chile peppers" (one L only), "hot peppers", or named as a specific variety (e.g., banana pepper). In many midwestern regions of the United States the Sweet Bell Pepper is commonly called a mango.[1] With the modern advent of fresh tropical fruit importers exposing a wider latitude of individuals to the tropical fruit variety of the Mango, this definition is becoming archaic. However many menus still call a stuffed Bell Pepper a Mango. In Mexico the term chile is used. Several other countries, such as Chile, whose name is unrelated, Perú, and Argentina, use ají. In Spain, heatless varieties are called pimiento and hot varieties guindilla. In Indian English, the word "capsicum" is used exclusively for bell pepper. All other varieties of chili peppers are called chili. In northern India and Pakistan, bell pepper is also commonly called "Shimla Mirch" in the native languages. Shimla incidentally is a popular hill-station in India (and "Mirch" means chili in native languages). In Polish, the word papryka is used for capsiscum fruit and dry spice (the word pieprz is used for black, red, and green pepper, but not for capsisum fruit or spice). In Hungarian, the word paprika is used for capsicum fruit and dry spice. In Israel capsicum is commonly called pilpel, meaning pepper in Hebrew.

Thanks very much,Roland.

In the US these are usually known as green bell peppers and yellow bell peppers. I would wager that not 1 in 10 Americans would know what a capsicum is. It is a scientific term for peppers.

Thanks very much Bob. can these green capsicums be called green pepers? and which name is more often used in your country?