Aperture is a word out of the camera vocabulary, I never really understood. However, in my photography class I just learned about it and got used to the term.
The Aperture is the opening of the camera. The bigger it is, the more light can pass through to the sensor. To describe how big the aperture is, we use f/stop numbers. Confusingly, the bigger the number, the smaller is the actual aperture. f/32 is a really small aperture while f/4 is a really small one. The aperture effects the size of the area in focus.
For my first picture I wanted everything to be in focus, so I chose a small aperture: f/25.
For the next two I wanted first the grass in the foreground, then the one in the background in focus. Therefore I chose the aperture to be large to create a deep depth of field. For these two I picked f/4.