The Memory connection is used to store the extracted dataset, for example, the dictionary table which can be used to lookup data in.
Read about using memory connection for lookup.
To create a Memory connection:
Step 1. Open Connections window.
Step 2. Click the
add connection button.
Step 3. Type in
memory and select the connection type.
Step 4. Name and save the connection.
while you can create multiple memory connections it really makes sense to have just one.