In Othello, so much of the action of the play is driven by the malicious influence of Iago and his schemes to destroy Othello. He organizes Cassio's fall from esteem and poisons Othello's regard for and faith in his wife. All three of these characters (Cassio, Desdemona, and Othello himself) are thus thrown into a point of crisis, relating to the loss (or perceived loss) of their honor and reputation, and they must grapple with the repercussions, ultimately to tragic results.
Cassio's loss of honor relates to the events of act 2, scene 3, when Iago manages to get Cassio drunk, before engineering events to implicate Cassio for the starting of a brawl. The fallout sees Cassio removed from his rank as Othello's lieutenant, and, for the remainder of the play, Cassio's primary motivation is to restore his previous position. To achieve this goal, he turns to Desdemona, hoping she could intercede with her husband on his behalf.
Meanwhile, there is also Iago's manipulations against Othello himself, as he influences Othello into doubting Desdemona's faithfulness, driving him into jealous suspicion against his wife (a suspicion that is further heightened by Desdemona's close contact with Cassio and intercessions on Cassio's behalf). In this respect, the story of Othello can be said to revolve around both male and female honor as it is (allegedly) under attack: the very suspicion that Desdemona is committing adultery is taken as a slight against Othello's own masculinity, but it is simultaneously framed as an infringement against her own honor and virtue. Meanwhile, Desdemona herself is left adrift, suddenly open to abuse and jealous accusations from her husband, with no understanding as to what could possibly lie behind these actions. In this respect, honor in Othello is coded along gendered lines. The supposed infringement against these gendered expectations culminates in the murder of the innocent Desdemona by her jealous husband's hand.