Quote Expiry refers to the period when a quote will remain valid before expiring. A quotation is normally valid for a set period of time.

You can add your default quotation expiry period and also adjust the Quote Expiry period on each individual Quote. 

Web Portal > Settings cog > > Accounts > Quotes > Quote Expiry > specify your settings (x number days, weeks or months) > Save.

App > Log in > Settings > Quotes > Quote Expiry > specify your settings (x number days, weeks or months) > Save.