Peak pulse and thermal headroom
The 1.5SMCJ90A: 1500W peak pulse capacity (10/1000µs waveform) tells you it absorbs a 1.5kJ transient event at the defined wave shape without degrading.
Package and deployment fit
Surface-mount DO-214AB (SMC) is the standard package for this power class of TVS — the lead frame handles thermal cycling without cracking the die bond. Unidirectional only — it protects one polarity, which is what you need for positive-going transients on a DC rail. Power-line protection is not rated for this device, so it sits in the general-purpose category rather than the mains-protection subclass — do not spec it as a primary AC line protector.