For those who don't know the word, a servlet is a small program, written in the Java programming language, that runs on a Web server, responding to the actions of online users.
The name is inspired by the word applet - already allowed in Chi - which is something similar, but it runs on the Web user's own computer, not the central server. In fact, the Oxford Dictionary of English defines a servlet as "an applet that runs on a server..." Applets are more visible to Internet users, and so the word applet became a little better known to the general public than servlet, although applets had their vogue mainly in the late 1990s / early 2000s.
Nowadays, servlets are probably more widely used than applets, but the word servlet is known only to IT people and others working with corporate systems. Nevertheless, it is listed by a few general dictionaries, and used widely enough to warrant its acceptance as a rare word.
There is a third word in this family, midlet, often written MIDlet, derived from Mobile Information Device. A midlet is, in fact, a Java program for a mobile phone or other small device. Such programs also had their day, but the word midlet never made it into the public consciousness. Nowadays programs for mobile phones are simply called apps.
