Enantiomers and couple of enantiomers

I ask myself a question for some time but it's impossible to me to find the answer!


I can't understand the difference when we say *" that molecule has a enantiomer "* and when we say *" has a couple of enantiomer ?"* 
\*That could by vague, here is an image (the molecule 1)[![enter image description here](https://i.stack.imgur.com/MNWJw.png)](https://i.stack.imgur.com/MNWJw.png)


Then, if I understood well this present molecule has *" 1 couple of enantiomer "* **and** *" 2 couples of diastereoisomers "* because it's a mesomeric compound RS, thus RS = SR.


But let us admit that I shall have taken one element with 2 asymmetric carbons : with 4 different compounds on each of the carbons (as the molecule 2) which is SR, I shall at this moment obtained \*\*"1 enantiomer "*: RS*, *2 diastereoisomers SS and RR*, and *" a couple of enantiomer "* *(= which is in fact the 2 diastereoisomers)*, it is good that please? 
*(I join an image also for more understanding.)* 


**Thank you in advance for every person who ventures to help me!**




According to the definitions



> 
> **[enantiomer](https://goldbook.iupac.org/html/E/E02069.html)**
> 
> 
> One of a pair of molecular entities which are mirror images of each other and non-superposable.
> 
> 
> 


and



> 
> **[diastereoisomerism](https://goldbook.iupac.org/html/D/D01679.html)**
> 
> 
> Stereoisomerism other than enantiomerism. Diastereoisomers (or diastereomers) are stereoisomers not related as mirror images. (…)
> 
> 
> 


I think it's best to use the terms *enantiomers* or *diastereoisomers* only when comparing two structures (or more eventually, for the latter term); as descriptive terms with opposite meaning (but it's more complicated, diastereoisomerism includes also e.g. *cis*/*trans* isomerism as well).


E.g. asking “How many enantiomers does this compound have?” can be confusing.


Also “(a) couple” might be confusing as well (in general language it can mean unspecific small number), I'd rather use term *enantiomeric pair* (even thought it's not an official term).


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