Electrode, secondary battery, battery pack, and vehicle

An electrode comprising an active material-containing layer which comprises an active material, wherein

• the active material comprises a plurality of primary particles comprising a niobium-titanium composite oxide,
• an average crystallite diameter of the plurality of primary particles is 90 nm or more,
• an average particle size (D50) of the plurality of primary particles is in a range of 0.1 μm to 5 μm, which is based on a particle size distribution chart according to a laser diffraction scattering method,
• an average value (FUave) of a roughness shape coefficient (FU) according to Formula (1) below is less than 0.70 in 100 primary particles among the plurality of primary particles, and
• each of the 100 primary particles has a particle size of 0.2 times to 4 times the average particle size (D50),
• [
• Formula
• 
• 
• 1
• ]
• FU
• =
• f
• f
• c
• =
• 4
• 
• π
• 
• 
• a
• 
• 
• 2
• (
• 1
• )
• where l represents an outer circumference length of a projected cross-section of each of the 100 primary particles, and a represents a cross-sectional area in the projected cross-section of each of the 100 primary particles.