Traditionally a role filled by a sister or closest friend.
The bride relies most on her maid of honor. Before the wedding, the maid of honor duties includes arranging bridesmaids' activities such as organizing the bridal shower and hen- do. She is also likely to attend planning meetings, dress fittings and so forth.
On the wedding day, the maid of honor is there to attend to the bride. She helps the bride with her dress and veil during the day, holds the bouquet when needed, and signs the marriage license as a witness (usually).
As the name implies it’s an honour to be given this role.