All IPv4 IPs which we use, consists of 32 bits which is represented with 4 decimal numbers separated by dots(.) for easiness in reading writing and remembering.
For example :
10.11.12.13 is an IP which represents 00001010.00001011.00001100.00001101 in binary.
The 4 separate decimals are 4 classes of the IP as per classless convention..
So, for IP 10.11.12.13...
10 = A Class
11 = B Class
12 = C Class
13 = D Class
Now about C Class IPs
In terms of SEO(SEO hosting more specifically) C Class IPs implies Different C Class IPs, more clearly IPs on different C Classes.
For example IPs 184.108.40.206 and 220.127.116.11 are same C Class as 1.1.1 is common in both.
But IPs 18.104.22.168 and 22.214.171.124 are on different C Class as they are on different c classes 1.1.1 and 1.1.2 respectively.
Similarly 126.96.36.199 and 188.8.131.52 are on different B Classes.
184.108.40.206 and 220.127.116.11 are on different A Classes.