What is ERISA and what's the difference between ISA& 401

[Ducklin]

I am new in this field and doing my own research to get more insight into the current pension scheme and the pension review that is going on after the collapse of Enron.
Some people mentioned ERISA, please excuise my stupidity, but what does ERISA stand for and how different is it to 401(K)? Also, some senior mentioned that some employees should switch from 401(K )to ISA (as the person changed company and would like to roll over his fund) What does ISA stand for and is it true that 401K charges higher admin fee than ISA?

Thanks for all the professional seniors for teaching me the differences between all the plans/products that's in the market for pension in this forum.

[exactuary]

ERISA = Employee Retirement Income Security Act of 1974 including numerous amendments since 1974. It includes tax, fiduciary, disclosure, minimum funding and federal insurance (Pension Benefit Guaranty Corporation) rules for retirement plans.

401k is one section of the Internal Revenue Code. It is part of the tax rules of ERISA.

IRA (not ISA) is an Individual Retirement Account created by ERISA. 401k is a DC (defined contribution) plan for groups of employees. IRA is a DC plan for individuals. The amount of tax deductible money that can be put into a 401k in one year for an employee is usually much greater than the amount that an individual employee can put into his own IRA.

401k plans cover groups of employees. When employment ends (or thereafter), an employee can usually rollover the value of his plan balance into an IRA.

IRA administration is usually more costly than 401k due to economies of scale.

[Ducklin]

Thanks exactuary, so, after terminating employment with a company, the fund in the 401(K) of the ex-employee will be rolled over into the IRA account until he finds another job at another company and then joins the 401(k) plan of the new company, is that correct? Or would the fund remain in the IRA if the person wishes to?
So, an IRA would give the ex-employee higher sum upon retirement?
My sincerest apology for my stupidity, I was reading the forum on comparison between DC plan and DB plans and it seems to be that DC plan is more preferred by current employer due to lower admin cost (as max. contribution by employer is at a set rate, ie. at 2%)
What would a retired person receive at the end of the plan (retirement age met!) with a DC plan (a lump sum of say $100,000 and thus prefer DC plan because the amount he receives in one go is HUGE?) or is this the case for a DB plan? I suppose that one of those plans (either DB or DC) will give out monthly annuity.

Thanks for your guidance in advance

[Ducklin]

Another point which I am confused with is, what impact would it have to an employer choosing a DB plan rather than DC plan AFTER the employee leaves the job?