“lel” is a common term used among people who frequent certain online imageboards. It is commonly used as schadenfreude in response to something bad happening to someone else, or some antic that elicits inappropriate laughter, implying the emitter of the laugh is a “troll.”
It has had a complicated history. The original acronym, “lol”, stood for “laugh out loud” and quickly replaced simulating laughter online. In the massively multiplayer online game World of Warcraft, there are two factions, Horde and Alliance. While their chat messages appear to each other while standing nearby in-game, the two factions cannot communicate with each other, which the server facilitates by running dialogue through a coder. When a Horde player types “lol” in chat, it appears to Alliance players as “kek,” which in itself is accepted as a sound made by silly laughter, especially when repeated (kekkekkekkek).
Soon, kek became itself used as to indicate inappropriate laughter, until it morphed back into “lel,” as k is next to l on the keyboard, and it also looks like a bastardation of “lol.”
There exists a type of Turkish snack food called “Topkek,” which the boards have since adopted as an higher-tier substitute for “kek.” Even this usage has now morphed into “Top lel” among groups of friends who have ventured deep enough into the imageboards.