In LOR, many spells have specific effects when overcasted. Overcasted refers to automatically casting spells levels higher than its original cast. When you do so, you use spell slots of that higher level
In the spell table, overcasted rules often are read as
4(+2) for example.
To understand this, the first number shown is the first level in which the additional effect is gained. The brackets symbolise additional level afterwards that effect stacks on. So for the example, when thst spell is overcasted as a 4th level spell and for every 2 level afterwarss it gains that bonus.
The other way is by a number which states what level overcasted would that spell gain that effect.
heightenind is a mechanic used to describe automatically overcasting of spells while using lower level spell slot. Spells and cantrips are automatcially heightened based on this
Your cantrips are overcasted to (your combined spellcaster level/2, rounded up). So at 9th level, your cantrips are caster to level 5.
Spells are overcasted to (Your highest spell level/2), rounded down. So if your highest level spell is level 5, your level 1 spells are casted as iif they are overcasted to level 2.