A variable geometry turbine comprising: a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls (24, 25); and a ring-like seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) axially movable across the annular inlet to vary the size of a gas flow path through the annular inlet, the annular inlet being divided into at least two axially offset inlet portions (26a, 26b, 26c); a plurality of apertures (94; 100) distributed about at least a portion of a circumference of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108); characterised in that: an axial extent of a free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) varies in magnitude around a circumference of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) to define a plurality of recesses (92; 98) located around the circumference of the free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108), and wherein a circumferential position of at least one aperture (94; 100) is different from a circumferential position of at least one axially adjacent recess (92; 98); and/or a circumferential position of each one of a plurality of apertures (94; 100) is different from a circumferential position of each one of a plurality of respective axially adjacent recesses (92; 98). a turbine wheel mounted for rotation about a turbine axis within a housing, the housing defining an annular inlet surrounding the turbine wheel and defined between first and second inlet sidewalls (24, 25); and a ring-like seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) axially movable across the annular inlet to vary the size of a gas flow path through the annular inlet, the annular inlet being divided into at least two axially offset inlet portions (26a, 26b, 26c); a plurality of apertures (94; 100) distributed about at least a portion of a circumference of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108); characterised in that: an axial extent of a free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) varies in magnitude around a circumference of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) to define a plurality of recesses (92; 98) located around the circumference of the free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108), and wherein a circumferential position of at least one aperture (94; 100) is different from a circumferential position of at least one axially adjacent recess (92; 98); and/or a circumferential position of each one of a plurality of apertures (94; 100) is different from a circumferential position of each one of a plurality of respective axially adjacent recesses (92; 98). an axial extent of a free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) varies in magnitude around a circumference of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108) to define a plurality of recesses (92; 98) located around the circumference of the free end of the seal (42; 48; 54; 60; 62; 64; 66; 68; 72; 76; 84; 86; 90; 96; 102; 104; 108), and wherein a circumferential position of at least one aperture (94; 100) is different from a circumferential position of at least one axially adjacent recess (92; 98); and/or a circumferential position of each one of a plurality of apertures (94; 100) is different from a circumferential position of each one of a plurality of respective axially adjacent recesses (92; 98).