Context: a knightship is a glider (a structure that translates itself across the Life grid periodically) which moves 2 horizontal units for each 1 vertical unit (or vice-versa if rotated). This is in contrast to e.g. the most popular 3x3 glider which moves diagonally (1 for 1). A knightship is a type of oblique glider - one that doesn't move orthogonally (only horizontal/vertical) or 45º diagonally.
What makes this an elementary knightship is that it isn't built out of smaller discrete components, unlike (for example) the oblique glider Waterbear (http://conwaylife.com/wiki/Waterbear). It's the first elementary oblique glider discovered.
It also happens to move exactly 2 vertical units for each 1 horizontal unit of motion, and carries this out in 6 time-steps (the theoretical minimum). Thus, in some sense it has the simplest movement of any possible knightship.
What makes this an elementary knightship is that it isn't built out of smaller discrete components, unlike (for example) the oblique glider Waterbear (http://conwaylife.com/wiki/Waterbear). It's the first elementary oblique glider discovered.
It also happens to move exactly 2 vertical units for each 1 horizontal unit of motion, and carries this out in 6 time-steps (the theoretical minimum). Thus, in some sense it has the simplest movement of any possible knightship.