Correct spelling, explanation: the correct word is registration. It comes from the verb register. When forming a noun from register, we add the suffix -ation (as in information or celebration). Some people mistakenly add an extra -e and write registeration, probably because register ends in -er. However, English doesn’t form nouns in this way. So, the correct spelling is registration – without the extra -e after register.

Definition of registration:
Noun, the action or process of registering or of being registered
The registration for the online course closes at midnight, so make sure to sign up before the deadline.
You will receive a confirmation email after completing the event registration.

Collocations with registration:
Some of the most commonly used collocations include:
1. Online registration: the process of registering for something via the internet.
Online registration for the conference is open until next Friday.
2. Student registration: the process of enrolling students in a school, course, or university.
Student registration for the new semester begins next week.
3. Vehicle registration: the official documentation proving that a car or other vehicle is legally registered.
You must renew your vehicle registration every year.
4. Event registration: the process of signing up for an event such as a conference, seminar, or workshop.
Event registration closes two days before the workshop starts.

Incorrect spelling, explanation: since registration comes from the verb register, some people mistakenly believe that the noun should include the full root word and simply add -ation, forming registeration. However, in English, some words undergo slight changes when forming nouns (e.g., regulate → regulation but not regulateation). The only correct spelling is registration. Compare it to other words like demonstration or operation, which don’t keep an extra -e from their base forms either.