The utf8mb3 character set has these characteristics:

Applications that use UTF-8 data but require supplementary character support should use utf8mb4 rather than utf8mb3 (see Section 10.9.1, “The utf8mb4 Character Set (4-Byte UTF-8 Unicode Encoding)”).

Exactly the same set of characters is available in utf8mb3 and ucs2. That is, they have the same repertoire.

utf8 is an alias for utf8mb3; the character limit is implicit, rather than explicit in the name.

utf8mb3 can be used in CHARACTER SET clauses, and utf8mb3_collation_substring in COLLATE clauses, where collation_substring is bin, czech_ci, danish_ci, esperanto_ci, estonian_ci, and so forth. For example:

CREATE TABLE t (s1 CHAR(1) CHARACTER SET utf8mb3;
SELECT * FROM t WHERE s1 COLLATE utf8mb3_general_ci = 'x';
DECLARE x VARCHAR(5) CHARACTER SET utf8mb3 COLLATE utf8mb3_danish_ci;
SELECT CAST('a' AS CHAR CHARACTER SET utf8) COLLATE utf8_czech_ci;

MySQL immediately converts instances of utf8mb3 in statements to utf8, so in statements such as SHOW CREATE TABLE or SELECT CHARACTER_SET_NAME FROM INFORMATION_SCHEMA.COLUMNS or SELECT COLLATION_NAME FROM INFORMATION_SCHEMA.COLUMNS, users will see the name utf8 or utf8_collation_substring.

utf8mb3 is also valid in contexts other than CHARACTER SET clauses. For example:

mysqld --character-set-server=utf8mb3

SET NAMES 'utf8mb3'; /* and other SET statements that have similar effect */
SELECT _utf8mb3 'a';

For information about data type storage as it relates to multibyte character sets, see String Type Storage Requirements.