spell_scripts

Table spell_scripts:
Id - Spell Id from spell_template
ScriptName - Assigned script name in core

Assignment .sql file located in each repo under sql/scriptdev2/spell.sql

Used to add custom behaviour to any spell. List of all available hooks can be found in core in SpellScript.h. There are two types, SpellScript or AuraScript.

Examples:

Registering a script works using functions RegisterSpellScript, RegisterAuraScript or RegisterScript(this one is when its both aura and spellscript).
RegisterSpellScript<EntangleFankriss>("spell_entangle_fankriss");

The above registers the script to ScriptName "spell_entangle_fankriss".
And this is its script:

struct EntangleFankriss : public SpellScript
{
    void OnEffectExecute(Spell* spell, SpellEffectIndex effIdx) const override
    {
        if (effIdx == EFFECT_INDEX_0)
        {
            uint32 spellId = 0;
            switch (spell->m_spellInfo->Id)
            {
                default:
                case SPELL_ENTANGLE_1: spellId = SPELL_SPAWN_VEKNISS_HATCHLING_1; break;
                case SPELL_ENTANGLE_2: spellId = SPELL_SPAWN_VEKNISS_HATCHLING_2; break;
                case SPELL_ENTANGLE_3: spellId = SPELL_SPAWN_VEKNISS_HATCHLING_3; break;
            }
            spell->GetCaster()->CastSpell(nullptr, spellId, TRIGGERED_OLD_TRIGGERED);
        }
    }
};