请教AGAINST得用法

一遇到AGAINST就晕,就难以理解句子得意思,麻烦哪位有此词得用法在这里发布一下.

1.Declining values for farm equipment and land, the collateral against which farmers borrow to get through the harvest season, is going to force many lenders to tighten or deny credit this spring

2.Bank depositors in US are all financially protected against bank failure because the government insures all individuals 's bank deposits.

3.In metalwork one advantage of adhesive-bonding over spot-welding is that the contact, and hence the bonding, is effected continuously over a broad surface  as against being ata series of regularly spaced points with no bonding in between.

麻烦哪位NN总结一下?谢谢