Bond has many uses. Mortals often buy bonds (bonos), a type of debt certificate. In the financial and world of goverment, governments “issue” bonds, and mortals buy them.
So you give the government your money and the government has to pay you back by a specific date with interest. It is a way that governments raise money.
There can be “bonds” between a mother and her son (viniculos afectivos entre madre e hijo), for example. So there can be strong bonds of friendship between mortals.
Now for an expression: my word is my bond, meaning that what I commit to is not to be broken: it is a binding commitment. In Spanish there are options: mi palabra es sagrada/mi palabra es mi compromiso.
Many moons ago, in Britain, people did not write things down: if someone said he would do something, that was enough, and most mortals complied with the obligation.
So perhaps you “lend” money to the government by buying bonds, have strong bonds within your family and with friends, and someone´s word is enough to mean commitment.