Boot is any non-like-kind real property received by the taxpayer and is taxable to the extent there is capital gain.  “Cash boot” is the receipt of exchange proceeds by the taxpayer.  “Mortgage boot”, also sometimes referred to as “debt relief,” is the taxpayer having less debt on the replacement property or properties that they had on their relinquished property.  Cash or mortgage boot can be offset by the taxpayer adding outside cash to the replacement property purchase.  If the taxpayer wants to receive cash boot, it must be received either at the closing of the relinquished property or after they have purchased all property they are entitled to under the exchange agreement- which is generally the end of the exchange period. Read the full article, What is Boot?