Disease is a very slippery concept," it says.

It is a slippery concept, and the agenda has shifted with the times.

In search advertising, "supply" is a somewhat slippery concept.

'Now' is a rather slippery concept in this context.

Authenticity, now regarded as a slippery concept, has been virtually dropped from the movement's vocabulary.

It remains an (unacknowledged) slippery circular concept for him.

A slippery concept, when you really thought about it.

Best practice is a slippery concept in this field.

Although, as he now knew to his cost, success on Lalonde was a slippery concept to define.

Progress is a slippery but important concept here.