M&E, MEL, MEAL and MERL, What's the difference?

M&E, MEL, MERL and MEAL whats the difference?
While M&E is the oldest, other acronym such as MEL, MERL and MEAL have evolved in recent times to refer to an area of expertise.
While M&E stands for monitoring and evaluation, it is a continuous management function to guide the project and program towards its goal by assessing if progress is happening in the right direction. M&E can help spot the bottlenecks in implementation and identify unintended effects as well. M&E involves regular collection of data, analyzing it and then using it to make informed decisions about the program design, implementation and improvements.
MEL stands for Monitoring, Evaluation and Learning. MEL incudes all the components of M&E but goes little further to emphasize the importance of continuous learning and improvement. In addition to carrying out all the function required under M&E, MEL also places importance to learning from project and programs, sharing knowledge, and improving on the outcomes over time.
MEAL stands for Monitoring, evauation, accountability, and learning. It adds on accountability component to MEL framework. With emphasis on accountability, it aims that organizations are accountable towards it beneficiaries, donors, and other stakeholders. Information’s sharing with stakeholders and having a feedback mechanism forms an important part of accountability here. MEAL equally uses data to monitor progress and make decisions, learn from what went well and what went wrong, but adds accountability criteria of the organization towards its stakeholders.
MERL stands for Monitoring, Evaluation, Research and Learning and it expands on MEL framework with inclusion of research as a key component. In addition to everything that is included in MEL, it aims to promote the importance of rigorous research and analysis to improve design and implementation of the program or a project.
While, M&E, MEL, MERL and MEAL all use the fundamental concept of M&E, each one puts some emphasis on some part of it according to the need and nature of the project and program.