Hi Pradeep - happy to provide some more details. Meet-in-the-Middle Pattern Design is a pattern detailed in the PBE Patterns and Guidelines.
The key idea here is that we've identified an opportunity to create a pattern and that it makes sense to go ahead and build the pattern. As such, we want to design a pattern that is not only accurate, true and based on a representative solution - we also want to ensure that the pattern has the ease of use necessary for those that will consume it. What value is achieved if we create a pattern that is technically accurate, but cannot be understood or used by the pattern community?
To reach this goal we need to look at the design from two perspectives: A top down perspective, coming at the design from the perspective of the pattern user. The second perspective is to come at the pattern design from the bottom-up - using the elements of the reference solution to guide the creation of the pattern. We then meet--in-the-middle bringing these these two perspectives together.
If we focus only on top-down, we may miss key aspects of the pattern, and end up with a solution that is not true to the best practice. If we focus only on bottom-up we may end up with an unusable best practice. Balance and bringing the two perspectives together is necessary and vital.