What does X denote here?

MySQL, version numbers are organized as version = X.Y.Z. In Amazon RDS terminology, X.Y denotes the major version, and Z is the minor version number. For Amazon RDS implementations, a version change is considered major if the major version number changes—for example, going from version 5.1.71 to 5.5.33. A version change is considered minor if only the minor version number changes—for example, going from version 5.5.31 to 5.5.33.

D

MySQL version = X.Y.Z

X = Major version, Y = Release level, Z = Version number within release series.

From the Amazon RDS standpoint, a version change would be considered major if either major version or release level is being changed. Example: going from 5.6.X -> 5.7.X.

A version change would be considered minor if the version number within the release is being changed. Example: going from 5.6.27 -> 5.6.29.

https://aws.amazon.com/rds/mysql/faqs/

D. (ANS)

he naming scheme in MySQL 5.5 uses release names that consist of three numbers and an optional suffix; for example, mysql-5.5.1-m2. The numbers within the release name are interpreted as follows:

The first number (5) is the major version number.

The second number (5) is the minor version number. Taken together, the major and minor numbers constitute the release series number. The series number describes the stable feature set.

The third number (1) is the version number within the release series. This is incremented for each new bugfix release. In most cases, the most recent version within a series is the best choice.

D.
major version

D