An authenticated security agreement is a writing (or electronic record) that provides a description of the collateral, the debtor's intent to grant a security interest, and the debtor's signature.
Authentication means signing something, including electronic signatures. UCC § 9-102(a)(7).
The description must be sufficient to describe the particular item, as defined in UCC § 9-108.
In a majority of states, inventory, accounts receivable, chattel papers, etc. are assumed to include future inventory, etc. However, this should not be relied upon.
A financing statement can also be a security agreement.
A financing statement is a record that is publicly filed to put other people on notice of a security interest in the collateral.
A financing statement does not have to be very specific.
A financing statement does not have to be signed.
UCC § 9-108(c) says the very generic from the financing statement will not work.
A security agreement can be oral. An authenticated security agreement cannot.
Sometimes people may disguise a security agreement as a "lease," but this is ineffective if it works as a security agreement. (Like if the property can be bought for $10 after paying the value plus interest.) UCC § 1-203.