Pen pals (or penpals or pen friends) are people who regularly write to each other, particularly via postal mail.

A penpal relationship is often used to practice reading and writing in a foreign language, to improve literacy, to learn more about other countries and life-styles, and to make friendships. As with any friendships in life, some people remain penpals for only a short time, while others continue to exchange letters and presents for life. Some penpals eventually arrange to meet face to face; sometimes leading to serious relationships, or even marriage.

Penpals come in all ages, nationalities and cultures. Pals may seek new penfriends based on their own age group, a specific occupation, hobby, or select someone totally different from them to gain knowledge about the world around them.

Most people writing to a penpal do not use their native language in their letters, with the exception of natives in Western countries.

A modern variation on the traditional penpal arrangement is to have a keypal and exchange email addresses as well as or instead of paper letters. This has the advantage of saving money and being more immediate, allowing many messages to be exchanged in a short period of time. The disadvantage is that the communication can be very ephemeral if the email messages are not routinely saved. Many people prefer to receive paper letters, gaining the satisfaction of seeing their name carefully printed on a thick envelope in the letterbox. Using postal mail, it is possible to trade coupons, swap slips, postcards, stamps and anything else light and flat enough to fit inside an envelope, often called "tuck-ins". Many penpallers like to trade sheets of stickers, notecards and stationery sets.

A pen (Latin penna, feather) is a device used to apply ink to a surface, usually paper, for writing or drawing. Historically, reed pens, quill pens, and dip pens were used in ancient period, with a nib of some sort to be dipped in the ink. Ruling pens allow precise adjustment of line width, and still find a few specialized uses, but technical pens such as the Rapidograph are more commonly used. Modern types also include ballpoint, rollerball, fountain, and felt or ceramic tip pens.

The main modern types of pens can be categorized by the kind of writing tip or point:

These historic types of pens are no longer in common use:

Ancient Indians were the first to use the pen. According to ancient text the earliest of pens made in India used bird feathers, bamboo sticks, etc. The old literature of Puranas, Ramayana and Mahabharta used this kind of pen roughly 500 BC.^{[citation needed]}Ancient Egyptians had developed writing on papyrus scrolls when scribes used thin reed brushes or reed pens from the Juncus maritimus or sea rush. In his book A History of Writing, Steven Roger Fischer suggests that on the basis of finds at Saqqara, the reed pen might well have been used for writing on parchment as long ago as the First Dynasty or about 3000 BC. Reed pens continued to be used until the Middle Ages although they were slowly replaced by quills from about the 7th century. The reed pen, generally made from bamboo, is still used in some parts of Pakistan by young students and is used to write on small boards made of timber.^{[citation needed]}

PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system. The articles on broadcast television systems and analogue television further describe frame rates, image resolution and audio modulation. For discussion of the 625-line / 50 field (25 frame) per second television standard, see 576i.

In the 1950s, the Western European countries commenced planning to introduce colour television, and were faced with the problem that the NTSC standard demonstrated several weaknesses, including colour tone shifting under poor transmission conditions. To overcome NTSC's shortcomings, alternative standards were devised, resulting in the development of the PAL and SECAM standards. The goal was to provide a colour TV standard for the European picture frequency of 50 fields per second (50 hertz), and finding a way to eliminate the problems with NTSC.