Biome components go in the components object of a biome file in the behavior pack: they shape the land, climate and mob spawning of a custom biome. This list has all 15 of them in Minecraft 1.26.50.4.
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Component
minecraft:climateSets the weather and warmth of the biome: how hot it is, how wet it is and how much snow piles up.minecraft:creature_spawn_probabilitySets how likely animals are to appear when new land in this biome is first generated.minecraft:humidityMarks the biome as damp or dry no matter what its climate says.minecraft:map_tintsSets the grass and leaf colors used for this biome when it is drawn on a map.minecraft:mountain_parametersTunes how mountains in this Overworld biome are shaped and covered.minecraft:multinoise_generation_rulesDecides where this biome appears in the Nether.minecraft:overworld_generation_rulesDecides how this biome appears in the Overworld: which climates it shows up in, and which biome takes its place for hills, rivers, shores a…minecraft:overworld_heightSets how high or low the land in this biome is and how bumpy it gets.minecraft:partially_frozenLeaves some spots unfrozen in an icy biome, giving patchy ice and snow instead of a solid sheet.minecraft:replace_biomesSwaps out part of one or more existing biomes with this biome, so you can add a custom biome into normal worlds.minecraft:subsurface_builderApplies a surface builder to the layers below the normal ground, for example to change underground blocks.minecraft:surface_builderPicks the blocks that make up the ground of the biome, such as the top layer, the layer below and the sea floor.minecraft:surface_material_adjustmentsMixes in other ground blocks in patches based on noise, for example gravel or coarse dirt spots in a grassy biome.minecraft:tagsAdds tags to the biome.minecraft:village_typePicks which style of village is built in this biome.