Various Magento Cache flushing methods

Question

There are a number of ways to flush Magento cache, with slight differences. I have always been a bit confused about these and often end up overdoing it when deleting the cache. This my understanding of it as it is but maybe someone could correct this and answer my questions. I am hoping this question could be a source covering all aspects of cache ... I haven't found another question here which answers all questions in one.

Selecting individual lines using checkboxes and selecting refresh Surgically deleting a particular area of cache.

Pressing "Flush Magento Cache" Same as selecting and refreshing ALL from above (BTW anyone know why this operation is referred to as flush and the previous as refresh?)

Flush Cache Storage Same as last option but also includes some cache which may be shared 'by other applications' What applications for instance?

Flush Catalog Images Cache and Flush Javascript/CSS Cache As the name suggests ... Is this included in either of the last 2 options? BTW I think it must be important to also flush browser cache if using this. Correct?

Deleting contents of /var/cache and /var/sessions The nuclear option ? ... Does this delete absolute everything including javascript/css and catalog images cache; or what is not covered by this? Is there any other folders which should be included when doing a manual delete. I seem to remember hearing about another folder but I can't remember which one.

If anyone else has any other questions they might want to edit this and add the questions.