For example in ASCII each character is coded on a single byte, so a varchar2(10) field would accept any 10 characters long word, whereas in UTF-16 where each character is coded on 2 bytes, the same field would only accept 5 characters long words.
In comparison, a varchar2(10 CHAR) would always accept 10 characters long words, be the character set ASCII or UTF-16 or any other one.
HTH & Regards,
ORA-000TK : No bind variable detected... Shared Pool Alert code 5 - Nuclear query ready .