The common meaning of سيام (Siam) in the dictionary is to abstain.
In the terminology of Shari’ah, Siyam’ means worshiping Allah(s.w.t) by abstaining from all activities that spoil the fast, from dawn to sunset.
This definition also includes abstinence from vanity and obscenity. Because the beloved Prophet (peace be upon him) said, ‘Fasting is not just about abstaining from food and drink; Rather, abstinence from vanity and obscenity is the name of Siam. So if someone abuses you or shows foolishness to you, then say to him (without retaliating against him), ‘I have fasted, I have fasted.’
[Sahih jami al saghir, Albani 5376]