Difference between floodlight and Google tag manager?
 

Custom Floodlight variables use the keys u1=, u2=, etc. For pushed tags, variable names will be pre-populated in the custom variable fields; you will need to configure these variables to pull the appropriate data by mapping them to Google Tag Manager variables. Make desired modifications to the tag, then click Approve.

The Tag Manager is actually a container that can load custom tracking tags as needed, whereas Floodlight tags ARE tracking tags.

Custom Floodlight variables use the keys u1=, u2=, etc. For imported tags, the variable names are pre-populated in the custom variable fields; You must configure these variables to retrieve relevant data by mapping them to Google Tag Manager variables. Make the desired tag changes, then click Submit.

Tag Manager is actually a container that can load custom tracking tags on demand, while Floodlight tags ARE tracking tags.