A connection represents a link from a Java application to a database. All SQL statements and results are returned within the context of a connection. Database statements that are executed within this context form a database session which forms one or more closed transactions. Especially in distributed applications, multiple concurrent connections may exist accessing the same values of the database. which may lead to the following phenomena (referred to as transaction isolation levels):

• dirty reads:
  reading values from table rows that are not committed.
  
• non-repeatable reads:
  reading table rows more than once in a transaction but getting back different data because other transactions have altered the rows between the reads.
  
• phantom reads:
  retrieving additional "phantom" rows in the course of repeated table reads because other transactions have inserted additional rows that satisfy an SQL WHERE clause
  

[Android Documentation]