Spoofing is where you fake what something really is, so that it appears as something different.
In the computer world there are four major areas of spoofing that people hear about currently or experience. The four are email spoofing, Facebook page spoofing, phone number spoofing and IP address spoofing.
Email spoofing is where people send emails that appear to come from a different address than theirs. Usually these are phishing emails that have links in them that take you to locations to steal your personal information including account numbers, passwords, social security numbers, etc. They are usually done by getting an email with a number of email addresses on it and then sending to that group, but changing the form address that shows to one of these addresses. Often you can tell when you hover over the from address on a PC (hover does not work on phone unfortunately) and seeing it has a different real address.
Facebook page spoofing is where the spoofers set up a Facebook page of a person that already has one and then sends friend invitations to everyone on the real Facebook page. Facebook appears to have gotten diligent on these and takes them down within 48 hours of creation. It was a way to get in the accounts of everyone who had friended the page but later last year Facebook announced they had fixed that security hole but apparently a number of spoofers have not heard. If you get a friend request from someone and think you rare already a friend a couple things that usually reveal it is a spoof. First they never have a picture associated with them for some reason. Second, they hardly have any friends and no info. Third wait a day or two before confirming and you will see them disappear on friend request list in Facebook, but the email will still be in your email as Facebook has no control once it is delivered.
Phone number spoofing is where the vhishers (voice phishers) place calls to you for questionable items and usually trying to steal identity information and make it appear to come from a local number. You see a local number on your phone, may even be a number of a friend (or one time I saw call was from my cell number) s you answer and it is about an insurance plan or extended car warranty (I just cannot imagine them really being willing to put a warranty on my 17 year old Saturn with 710,000 miles) or similar. I get calls regularly from people who think I called them and I have to explain no it was a spoofer out of my control. The good news is the government and telephone companies supposedly will control these in 2019.
IP address spoofing average users seldom hear about, but it is a way that networks are often attacked using IP address (the address given to equipment on the Internet) that is in an network to try to slip buy the firewall and then attack the network usually to shut it down.