IP addresses are the addresses assigned to devices and machines that show where they are located on the Internet.
IP is an acronym for Internet Protocol which is the rules used to send information through the Internet.
There are two versions of IP. IPv4 which came out about 1980 is the version mostly used now. However we have run out of addresses in version 4. Who knew back in 1980 that in 2014 everyone would be carrying cell phones that all connect to the Internet and that we would have tablets and laptops? And that we would be attaching appliances, thermostats and cars to the Internet. These all need different IP addresses. Since about 1998 version 6 of IP has been available. It has many more addresses but they are different than version 4 so it was slow to be adopted. It is now being adopted a lot and your devices today come ready to work with either version.
IP version 4 addresses are 4 numbers separated by periods. Each number can range from 0 to 255. Legal addresses in IPv4 look like 192.168.2.1 There are lots of rules on how these are set up but these are the limits. The other day I received a message supposedly from Yahoo that said my account had been accessed from 198.971.300.45 I already was sure the message was spam or junk but when I read the address it confirmed for me that it was spam. An IPv4 address cannot contain 300 or 971 as those are greater than biggest number allowed which is 255
IP version 6 addresses are much longer and use hexadecimal (base 16) numbers. They are 32 digits long and can contain the single digit numbers 0 through 9 and the letters a thru f (case is not considered so A and a are same thing). Each 4 numbers is separated from the next set of numbers (a-f are numbers in hexadecimal) by a colon ( : ). So a IPv6 address may look like 0fde:1234:a67d:5695:e3a9:0000:0000:1289 They can also be abbreviated with a :: when there is one or more groups of all zeros and leading zeros in each group can be dropped so that same address can look like fde:1234:a67d:5695:e3a9::1289 which is easier to read.
Sometimes knowing what IP addresses look like can make it easier to recognize spam.