The term rekt derives from the word "wrecked." In general, rekt is a slang used to define something that got completely destroyed or a person that experienced a catastrophic failure. However, the term may carry different meanings depending on the context.
In the world of blockchain and cryptocurrencies, rekt is used to describe a severe financial loss, caused by a bad trade or investment. To illustrate, let’s suppose Alice is trading on margin and opens a big leveraged long position. If the market goes down and she gets liquidated, we may say "Alice got rekt." So, rekt is often used to describe someone that got liquidated after losing a high-leveraged trade.
The slang may also describe an asset that lost too much of its value or a market that dropped significantly (e.g., "this coin is rekt," or "the market is rekt"). Taking another example, imagine that Bob made a heavy investment on a cryptocurrency token through an ICO. But when the token finally hit the market, they were trading at a much lower price than Bob paid during the ICO crowd sale. In such a scenario, we may say that the token got rekt, which resulted in Bob and all bagholders getting rekt as well.
Within the online gaming community, the term rekt is usually describing a player (or team) that was defeated in an embarrassing or silly way. Or someone that is losing very badly in a competition. But, the oldest use of the slang is perhaps the one originally found in British English, where rekt was used when referring to a person that got too drunk or messed up.