How is a single element of the training set called? This question is only about the vocabulary.

Do / can you say


data item
data sample
recording
sample
data point
something else


when you talk about elements of the training / test set? For example:


  The figure shows 100 data items of the training set.
  
  Database A contains the same data items as database B, but in another format.
  
  The remaining data items were removed from the dataset.
  
  Those 10 classes have 123456 data items.


Please provide papers with examples.

According to Google n-grams:
The term you are looking for is "Example".
Source: Martin Zinkevich, Research Scientist at Google (http://martin.zinkevich.org/rules_of_ml/rules_of_ml.pdf)

Instance: The thing about which you want to make a prediction. For example, the instance might be a web page that you want to classify as either "about cats" or "not about cats".

Label: An answer for a prediction task ­­ either the answer produced by a machine learning system, or the right answer supplied in training data. For example, the label for a web page might be "about cats".

Feature: A property of an instance used in a prediction task. For example, a web page might have a feature "contains the word 'cat'".

Example: An instance (with its features) and a label.