An orbit is the path around another object in space. The path is curved. The amount of curve depends on the relative size and speed of the two objects. The path can be open or closed, that is, a curve or an oval. No real orbit is a perfect circle.
This tool visualises in 3D a basic orbit to help better understand how an orbit is defined.
The tool presents a ‘Keplerian orbit’ around the Earth, this means it is an idealised orbit. The Earth is shown as a visual aid but the rotation of the Earth is not included.
You can read more Nibbles in Space at 
SpaceProf.xyz 
, with 000316 on ‘What’s an orbit?’. And, if you want to go into more depth at The International Handbook of Space Technology which is a definitive modern text on space technology with contributions from globally leading agency experts from NASA, ESA, JAXA, and CNES, as well as European and North American academics and industrialists. This comprehensive handbook provides an overview and a holistic understanding of the system-of-systems that is a modern spacecraft.