Literally: One. Unique. Sole.
A Name of Allah. Allah. One Whose perfect attributes encompasses everything. The One Who has no similar or like.
The Name of Wâhid negates and rejects the shariks in the attributes of Allah encompassing the universe and the creatures within it. As for the Name of Ahad, It denotes the oneness, unity and singleness of Allah in His Essence.
(Please refer to the article Al-Ahad)