Understanding the definition of ekklesia (and its alternate spelling ecclesia) is an important component of understanding the church. Ekklesia is a Greek word defined as “a called-out assembly or congregation.” Ekklesia is commonly translated as “church” in the New Testament. For example, Acts 11:26 says that “Barnabas and Saul met with the church [ekklesia]” in Antioch. And in 1 Corinthians 15:9 Paul says that he had persecuted the church [ekklesia]  of God.” The “called-out assembly,” then, is a congregation of  believers whom God has called out of the world and “into His wonderful  light” (1 Peter 2:9). The Greek ekklesia is the basis for our English words ecclesiastical (“pertaining to the church”) and ecclesiology (“the study of doctrine concerning the church”).  Source: https://www.gotquestions.org/definition-ekklesia.html 

 Ekklesia (or ecclesia) is a Greek term meaning "assembly" "gathering" or "called-out ones".  It refers to a group of people, not a building, historically used for  Athenian citizens gathering for public business and in the New Testament  to describe the church or community of believers summoned by God.  Key aspects of ecclesia include:

• Definition: Originates from ek ("out") and kaleo ("called"), literally meaning those called out.
• Biblical Use: Refers to the body of believers (the "Church") rather than a physical  structure, representing people united by a common purpose.
• Historical Context: In ancient Greece, it was a political assembly of citizens managing city affairs.
• Septuagint: The term appears in the Greek translation of the Hebrew Scriptures to denote the "assembly of Israel".

https://www.merriam-webster.com/dictionary/ecclesia

https://study.com/academy/lesson/ecclesia-ancient-greece-history-facts.html

https://www.episcopalchurch.org/glossary/ecclesia/

https://www.catholicculture.org/culture/library/catechism/index.cfm?recnum=1373

 he ekklesia is often translated as “church” and divided between  a sacred and secular definition. However, this translation and  separation loses the significance and nuances of the term. The etymology  of the word renders the ekklesia as an assembly of those who have been called out. The Greek usage of the word presents the ekkelsia as a political phenomenon in which the ekkelsia is an assembly that gathers to benefit the common good of the entire polis. Biblically, the ekkelsia is  often understood as an assembly of those who have been called by God  and has a spiritual, relational, geographical, and universal existence.  By evaluating the bibilcal usage of ekklesia within its Greek context, it becomes apparent that the biblical ekklesia is similarly for the purpose of seeking the common good. Unlike the Greek ekklesia, which seeks to benefit the polis in order to create a beneficial society, the biblical ekklesia is  intended to seek the common good in order that mankind might be saved  through Jesus Christ. For Christians, expanding the definition of ekklesia based on wider contexts means that first, believers must respond to the call to be a part of the ekklesia and be an active member of the assembly. Secondly, believers must seek the common good of those within and outside of the ekklesia through fulfilling the great commission by fulfilling the greatest  commandment. This requires involvement with the rest of the world,  rather than simply a weekly gathering. 

Source: https://digitalcommons.liberty.edu/jspp/vol1/iss1/12/