A co-loader typically refers to a company that works together with another company to move cargo from one place to another. A co-loading arrangement can take many forms, but generally, it involves two or more companies combining their cargo into a single shipment in order to fill a container or truck and reduce the cost of transportation for all parties involved.

A co-loader could be a 3PL (Third party logistics) company working as a intermediary between other companies and trucking companies. They work to match up loads in order to optimize the use of resources and reduce costs.

Another example would be when a freight forwarder works with multiple shippers to fill a container with cargo of various origins headed to the same destination, the freight forwarder acts as the co-loader consolidating different shipper's cargo into the same container, this way each shipper can share the cost of the container and increase the efficiency of the shipping process.

So "co-loader" in transportation refers to the companies or entities who work together to move cargo, usually by consolidating multiple small loads into a single shipment, thus optimizing resources and lowering costs for all parties involved.