What is the difference between Fedora, Red Hat and CentOS ?

Practically there is no difference. All these are from same mother i.e upstream.

Fedora : Its an free version of Linux developed by Red Hat/Fedora community. Its user-friendly and NOT production ready.

Red Hat : Red Hat Enterprise Linux(RHEL) is leader in Enterprise Linux server. It is 100% production ready and Red Hat provides full support for this using there subscription model that means we need to pay for support only not for product.

Cent OS : CentOS is replica of RHEL but they don't have support so its risky for Enterprise customers. Good for testing purpose .

RHEL is a commercial distribution, while CentOs&Fedora is a community distributions.

Both CentOs & Fedora supported by Red hat, basically CentOs is RHEL but with community support instead, while Fedora is an upstream distribution, meaning you always get the new software release without prior testing.