  Chiral magnets can host topological particles known as skyrmions, which carry
an exactly quantised topological charge $Q=-1$. In the presence of an
oscillating magnetic field ${\bf B}_1(t)$, a single skyrmion embedded in a
ferromagnetic background will start to move with constant velocity ${\bf
v}_{\text{trans}}$. The mechanism behind this motion is similar to the one used
by a jellyfish when it swims through water. We show that the skyrmion's motion
is a universal phenomenon, arising in any magnetic system with translational
modes. By projecting the equation of motion onto the skyrmion's translational
modes and going to quadratic order in ${\bf B}_1(t)$, we obtain an analytical
expression for ${\bf v}_{\text{trans}}$ as a function of the system's linear
response. The linear response and consequently ${\bf v}_{\text{trans}}$ are
influenced by the skyrmion's internal modes and scattering states, as well as
by the ferromagnetic background's Kittel mode. The direction and speed of ${\bf
v}_{\text{trans}}$ can be controlled by changing the polarisation, frequency
and phase of the driving field ${\bf B}_1(t)$. For systems with small Gilbert
damping parameter $\alpha$, we identify two distinct physical mechanisms used
by the skyrmion to move. At low driving frequencies, the skyrmion's motion is
driven by friction, and $v_{\text{trans}}\sim\alpha$, whereas at higher
frequencies above the ferromagnetic gap, the skyrmion moves by magnon emission,
and $v_{\text{trans}}$ becomes independent of $\alpha$.
