1 [U] the act of inviting sb or being invited 邀请:
Entry is by invitation only.凭请柬入场。a letter of invitation邀请信
2 [C] an invitation to sb/sth (to sth/to do sth) a written or spoken request to go somewhere or do sth 邀请书;口头邀请:
Did you get an invitation to the conference?你接到会议邀请函了吗?a wedding invitation婚礼请帖
You may accept an invitation, or you may turn it down or decline it. 接受邀请可以说accept an invitation,拒绝就用turn it down或decline it。