In the simplest terms, cohesion is the process of linking and connecting sentences together. Cohesion is considered the relationship between two elements (clauses, words, or phrases) in written or oral text.
(koʊˈhi ʒən) n.
1. the act or state of cohering, uniting, or sticking together.
2. the molecular force between particles within a body or substance that actsto unite them.
3. Bot. the congenitalunion of one part with another.
4. Ling. the property of unity in speech or writing that stems from links among surface elements, as in the reference of pronouns to elements in the surrounding discourse.