I think I don't get the meaning of "enriched" in the context of genes. What's the difference of gene being "enriched" and "expressed" in the cell?
In most cases (i.e. assuming there is no aneuploidy) a gene won't be enriched, however, the transcript from a gene may be enriched. A synonym in this case would be overrepresented. In other words, you find relatively more of the transcript compared to other transcripts.
Since you seem to confused about the difference between transcripts and genes, I highly recommend working through the material on a site like Khan Academy. This will help you understand the basic vocabulary and concepts of molecular biology. There are also a number free online textbooks available at NCBI where you can get more in depth information.
In the context of transcriptomics the term 'enrichment' is usually connected to differential analysis:
- If a transcript (or some/all transcripts of a gene) are detected in a given sample that transcript is expressed
- If a transcript is detected at (statistically significant) higher levels in sample (or condition) A compared to another sample B, that transcript is enriched in sample A.
In some cases one might compare two cell types, where only one expresses a given transcript, in this expression and enrichment in that cell line (compared to the other one) would be almost the same.