Eigenvectors characterise a linear transformation by answering a simple question: What lines map to themselves after the transformation? Say for example you ro

Eigenvectors characterise a linear transformation by answering a simple question: What lines map to themselves after the transformation? Say for example you rotate something in 3D. The rotation axis remains unchanged. That's an eigenvector. Or say you mirror something in 3D, then all the lines lying in the mirror plane remain unchanged (all eigenvectors with eigenvalue 1), and the line orthogonal to the mirror plane remains unchanged - or rather, flipped, so it's an eigenvector with eigenvalue -1.