What are genes?

In this slide there is a brief explanation of what are genes. For that we have to understand what is a cell and what are chromosomes. Here are some more definitions:

Cell: The basic unit of life. Our body is made of cells. Each cell has a nucleus and inside the nucleus there are things called Chromosomes. 

Chromosome: are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

Here is a video:

And here is the definition that we saw in class.

Some more pictures that can help you:

Another:

We have 23 pairs of chromosomes.