In this contribution we discuss the process of understanding “integration” in a context of migration and arrive at the conclusion that the term integration, appears to be a case of valuable vagueness of terminology in EU document REGULATION 516/2014 and beyond. We use the framework of sociocognitive terminology studies (SCTS) to discuss vagueness of the unit of understanding (UoU) “integration”. Within the European Union, collective cognition is constructed and widely discussed leading to new units of understanding and terminological neologisms. In general, final drafts of EU documents are meant to represent the collective voice of all individual Member States. A degree of vagueness allows these Member States to agree on measures such as the establishment of a European Integration Fund (EIF), resulting in REGULATION 516/2014, without sacrificing their respective issues, goals, and priorities. We observe and describe the EU-understanding of “integration” of immigrants by taking a mixed method strategy leading to triangulation of results obtained by a) taking note of publications by legal specialists on the history of the European integration policy and on the role of vagueness therein, b) qualitative terminological analysis of knowledge rich text fragments in European REGULATION 516/2014 and c) consulting research results on the transposition and implementation of the European UoU “integration” in one EU member state, Belgium. We finally suggest Cognitive Sociolinguistics and SCTS to join forces with Legal Linguistics to study meaning in EU law.