Admission or joining of a society, club, or organization; becoming a member (often expressed as 'to join' with する).
大学のテニスサークルに入会した。
I joined the university tennis club.
入会の際には身分証明書の提示が必要です。
You need to show identification when joining.
入会金はいくらですかと受付で聞いた。
I asked the reception how much the membership fee was.