Sajda or السجدة means prostration and is an act of worship.
Sajda or السجدة (the Arabic singular of السجدات and also related to the act of prostrating "sujud" السجود) means prostration and is an act of worship.
One usually performs sujud during the daily prayers. One can do a sujud of shukr (prostration of thankfulness). And one is recommended to do sujud when passing by some special verses during the Qur'an recitation.