Engrailed Cross and Indented Cross
For the Engrailed Cross (Fr: Croix Engrelée or Croix Engreslée), the obvious feature is the rugged edges of each arm.
'Engrailed' simply means dimpled with concave curves, similar to the convex curves seen on the edge of a scallop shell (see Compostelan Cross). Grail reminds us of the Holy Grail; the cup used by Jesus at the Last Supper (see Communion Cross).
The word 'engrailed' is distantly related to grill, implying protection. (Actually, grill is not such a neat analogy for Christians, since although a grill can protect something precious, the precious gift of salvation is not locked away but freely available. Indeed, the cross can make us free.)
The pattern also looks a bit like waves on the ocean; hence an alternative name: Wavy Cross. (See also a more recent Wavy Cross.)
The feature of the Engrailed Cross in a Christian context is its spikes, which represent the thorns piercing Jesus' head during his Crucifixion (see Crown of Thorns Cross).
A similar heraldic cross, but with the spikes pointing inwards, is called the Invected Cross. Christians might refer to this as a Paternoster Cross.
Indented Cross
A heraldic cross with the spikes pointing both inward and outward resembling the teeth, or rather the dentures, of a dolphin, is called an Indented Cross (Fr: Croix Denchée or Croix Vivrée).
Where the teeth angles are more acute it is called a Dancetty Cross (Fr: Croix Écotée). Both the Indented and Dancetty Crosses look similar to the Flaming Cross.