In short, an elliptical construction is one where we leave something out.
Often we do this to avoid repeating a word of a phrase. Here are some examples to show what I mean. In these examples you can leave out the words that are in the square brackets.
Leaving out a noun
Kristy attended the conference last week; Prakash attended [the conference] too.
Leaving out a verb
She enjoys dramas, and he [enjoys] comedies.
Leaving out a verb-phrase
The sales team went to the conference, but marketing didn’t [go to the conference].
These constructions are useful when we list statistics or figures.
In 2011, the company made 10% profit; in 2012, 12%; and in 2013, 14%.