A cryptocurrency address is like an email address, but instead of being fused or emails, it is to send and receive cryptocurrency. Usually, cryptocurrency addresses are derived from a public/private key pair and are between 16 and 24 characters long consisting of a random collection of numbers and letters. Cryptocurrency addresses are also often embedded into QR codes to make sending cryptocurrency easier. Because cryptocurrency addresses are for receiving cryptocurrency, it is ok to post them anywhere and people can then send you cryptocurrency.
An example of a Bitcoin address is: 3MfesBVoKWMkfYp56Ji8WVSWrLhY6ua5aq
An example of an Ethereum address is: 0xFE75716f9aFB0ABa1a02A834BFDd7019c52E8F24