1. working together simultaneously
working in tandem with our consultants/clients/customers
This idiom refers to somebody or something working or happening together, at the same time; or things that are linked in some way. It can be used in a social context, but it is much more common in a professional one where two or more people or pieces of equipment - computers, for example - that are linked or working closely together are frequently said to be 'in tandem.' Phrases with a similar meaning include 'side by side,' and 'work shoulder to shoulder.'