Param Ishwar(परम ईशवर) or Parameshwar(परमेश्वर) means Universal Lord or Ultimate God. Param means universal, ultimate, absolute, or supreme. Ishwar means God.
The Hindu trinity, also known as Sanatan Trinity, is composed of (Param)Brahma, (Maha)Vishnu, and (Maha Ishwar)Shiv. All three gods in the Hindu Trinity can be seen as the Universal God, it's all a matter of perspective of the scripture you read.
For devotees of Brahmaism, Brahma usually refers to Param Brahma(a form of Brahma) which is the all-pervading aspect of God, often called "the all-pervading world-soul." Since everything comes from God, it is not different from Him. Scripture states "everything is Brahma." This sat (true/eternal) aspect of God is realised by understanding one's own eternal nature as atman.
Brahma is also known as the Creator.
According to the Bhagavad Gita, Krishna(a from of Vishnu) is Param Brahma.
Vishnu is also known as the Maintainer/Sustainer.
For devotees of Maheshwar(a form and title of Shiv), Shiv is the Universal God.
Shiv is also known as the Destroyer. All natural disasters like Tornadoes and earthquakes are attributed to his anger.