Theta this, theta that

[Flynrider]

When looking at a potential trade, some spreads or ICs have either positive or negative theta. Do i understand it correctly that a negative theta would indicate that the option does not deteriorate over time or is time decay adverse?
Thanks.

Theta is rate of change for extrinsic value only (iow time value). Some single options or spreads will only ever have extrinsic value (e.g. single short options, or short strangles), so will never go -ve theta. I think most spreads (verticals, calendars, IC etc.) or single options involving long options can be either +ve or -ve theta depending on strikes, dates, UL price, IV etc.