Block components go in the components object of a block file in the behavior pack: they decide what a custom block is and does. This list has all 49 of them in Minecraft 1.26.50.4.
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Component
minecraft:block_entityGives each placed copy of the block its own saved data, so one block can remember things that its neighbors do not.minecraft:breathabilityDecides if mobs and players can breathe inside the block.minecraft:chest_obstructionDecides whether this block stops a chest underneath it from opening.minecraft:collision_boxSets the solid part of the block that players, mobs and items bump into.minecraft:connection_ruleControls whether fences, walls, iron bars and glass panes join up with this block when placed next to it.minecraft:crafting_tableTurns the block into a crafting station that opens the 3x3 crafting screen.minecraft:destructible_by_explosionControls how well the block stands up to TNT, creepers and other blasts.minecraft:destructible_by_miningControls how long it takes to break the block by hand or with tools.minecraft:destruction_particlesSets the little pieces that fly out when the block is broken.minecraft:display_nameSets the name players see for the block in the inventory and tooltip.minecraft:embedded_visualSets how the block looks when it sits inside another block, for example when it is planted in a flower pot.minecraft:entity_fall_onSets how far a mob or player must fall onto this block before landing on it counts, so scripts can react to the landing.minecraft:flammableLets nearby fire spread onto the block and burn it away, like wood.minecraft:flower_pottableLets the player put this block into an empty flower pot.minecraft:frictionSets how slippery the block is to walk on, from 0.0 to 0.9.minecraft:geometryPicks the 3D model that draws the block.minecraft:instrument_soundPicks the sound a note block makes when this block is above or below it.minecraft:item_visualSets how the block's item looks in the hand and inventory, by giving it its own model and textures.minecraft:leashableLets players tie a lead to the block, like a fence post.minecraft:light_dampeningSets how much light the block soaks up as light passes through, from 0 to 15.minecraft:light_emissionMakes the block glow, from 0 (no light) to 15 (as bright as a torch or glowstone).minecraft:liquid_detectionDecides what happens when water touches the block: it can hold water inside (waterlog), let water flow through, or break.minecraft:lootPicks the loot table that decides what drops when the block is broken.minecraft:map_colorSets the color of the block when it is drawn on a map.minecraft:material_instancesAssigns textures and render settings to the faces of the block's model.minecraft:movableControls what happens when a piston pushes or pulls the block.minecraft:on_fall_onRuns a block event when a mob or player lands on the block.minecraft:on_interactRuns a block event when a player uses (right clicks or taps) the block.minecraft:on_placedRuns a block event right after the block is placed.minecraft:on_player_destroyedRuns a block event when a player breaks the block.minecraft:on_player_placingRuns a block event while a player is placing the block.minecraft:on_step_offRuns a block event when a mob or player steps off the block.minecraft:on_step_onRuns a block event when a mob or player steps onto the block, handy for pressure plates or traps.minecraft:placement_filterLimits where the block can be placed and makes it break if its support goes away, like a flower that needs dirt below it.minecraft:precipitation_interactionsDecides how the block deals with rain and snow falling on it.minecraft:queued_tickingRuns an event after a delay, either once or again and again.minecraft:random_offsetShifts the block a little from the center, by an amount picked from its position, like flowers and grass that are not lined up perfectly.minecraft:random_tickingRuns an event now and then at random times, the same way crops grow.minecraft:redstone_conductivitySets how the block behaves with redstone around it.minecraft:redstone_consumerLets the block receive redstone power so scripts can react when the signal changes.minecraft:redstone_producerMakes the block give off a redstone signal, like a redstone block or a lever that is on.minecraft:replaceableLets another block be placed right where this one is, replacing it, the way placing a block on tall grass or snow layers swaps them out.minecraft:selection_boxSets the part of the block the player can point at and click, shown by the outline.minecraft:soundPicks the set of sounds the block makes when it is placed, broken and walked on.minecraft:supportGives the block the support shape of a fence or stairs, so other blocks can attach to it the same way.minecraft:tagsAdds tags to the block so tools, recipes and scripts can find it by group, like "minecraft:is_pickaxe_item_destructible".minecraft:tickMakes the block run its tick event after a delay, once or over and over.minecraft:transformationMoves, turns or resizes how the block looks, around the center of its space.minecraft:unit_cubeDraws the block as a plain full cube.