A Log4j is an open-source logging library commonly used by apps and services across the internet. If left unfixed, attackers can break into systems, steal passwords and logins, extract data, and infect networks with malicious software.
Cross site scripting (XSS) is an attack in which an attacker injects malicious executable scripts into the code of a trusted application or website. Attackers often initiate an XSS attack by sending a malicious link to a user and enticing the user to click it.
SQL injection is a web security vulnerability that allows an attacker to interfere with the queries that an application makes to its database. It generally allows an attacker to view data that they are not normally able to retrieve.
It's typically used to imply that someone has been controlled or compromised, for example "I was pwned in the Adobe data breach".