Parameshwara or Parameshwar, also transliterated from Sanskrit in other ways, is a Hindu concept literally meaning the Supreme God. The word "param" meaning the highest is added to Ishwara to intensify the title of God.
Same as Absolute Reality or Absolute Truth (See Para Brahman. The term Parameshwara (Supreme Lord) is used specifically indicate The Supreme Personality of Godhead, who is also the “supreme controller”. This is generally so in order to stress superiority over the contrasting term Maheshvara (Great Lord). And yet it is common that in many Vedic scriptures the term Ishvara is used as a short form for Parameshwara. Many Hindu text like Shiva purana and Linga purana describes Shiva along with Parvati as 'Parvathi Parameshwara'. Here parameshwar is mentioned as the husband of mother goddes Parvathi. Also note that the term Maheshvara is also used as a synonym to denote Lord Shiva. Brahma Samhita declares Krishna as Parameshwara:
Isvara paramah krishna sac-cid-ananda vigrahah anadir adir govindah sarva karana karanam. This is according to the school of Advaita Vedanta.
Lord Krishna (Vishnu) is the supreme absolute controller, whose form comprises immortality, omniscience, and bliss. He is without beginning, the origin of all, the cause of all causes and the source of the Vedas. (Brahma Samhita 5.1) .[1]