what is common prayer?

Like the phrase "Christian", we use "common prayer" often enough, but perhaps when we try to fix it we end up with a spectrum with different masses and groups having varying edges beyond which their definition stops.

So - what is common prayer? For the use of this post, not a rhetorical question but a discussion opener. Everyone using the like words, ritual, robes_ we are probably all happy that that is common prayer.

But what about:

1) Using the like speech with significantly different ritual and understanding. Eg. two Anglican churches using 1662 in the 1950s - exactly the like words, but one following Anglo-Catholic understanding, with eucharistic vestments, incense, etc. and the former in cassock, surplice, and scarf at the N end of the table_

2) Using different translations of the same text. Rite 1 and Rite 2 (Elizabethan and contemporary English) in TEC`s BCP. This Sunday, TEC`s translation cf. the current RC translation of the same Latin collect. The NZ RC Office translation is unlike to the USA RC Office translation - both are authorised. Other translations of the same text (eg. Universalis) are not authorised. The Vatican does not see them as satisfying the necessity to beg the office.

3) Praying different texts. Different eucharistic prayers from the same prayer book or missal. Is it common prayer merely because these are bound together in the same volume? Or authorized by the same office? The NZ Anglican prayer book has different eucharistic rites with scarcely any resemblance to each other, at least verbally. NZ Anglicans can be praying quite different texts as their daily office - all authorised. If one individual is praying one set of psalms and another individual is praying another set are both praying "the appeal of the Church"? RC monasteries regularly end up praying quite a different choice of psalms than RC priests, yet both would consider themselves as praying "the appeal of the Church", common prayer.

4) Following different readings. NZ Anglicanism has various different lectionaries authorised, with options within each. Does the RC Extraordinary Form be the 3 year lectionary or use the traditional one?

What do you remember? What is common prayer?