Let's Encrypt (www.letsencrypt.org) is a free, automated and open certificate authority. What that means is that Let's Encrypt provides a mechanism to install secure socket layer (SSL) certificates on computers for free. SSL certificates are the mechnism used to secure traffic on the Internet. If you have used a website with the https:// prefix you the webserver and web browser are using SSL certificates to encrypt your communications.
Let's Encrypt has provided this service which in the past cost money for free, because having all traffic on the Internet encrypted even non-sensative information is a GOOD THING.
If you have a website you should implement SSL certificates if you have not done so already.
If you do not know if you do or not, then ask your IT consultant.